GIFT  OF 
Agriculture  education 


THE 


FIRST  YEAR  OF  SCIENCE 


BY 


JOHN  C.  HESSLER,  Ph.  D. 

\ s 

PROFESSOR  Or  CHEMISTRY,  THE  JAMES  MILLIKIN   UNIVERSITY. 

LATE  INSTRUCTOR  IN  THE  UNIVERSITY  OF  CHICAGO  AND 

IN  THE  HYDE  PARK  HIGH  SCHOOL,  CHICAGO 


nblX  aUd 


BENJ.  H.  SANBORN  &  CO. 
1914 


1 

144 


COPYRIGHT,  1914 

BY 
JOHN  C.  HESSLER 


HGRIC,  DEPT, 


Ur" 


R.  R.  DONNELLEY  &  SONS  COMPANY 
CHICAGO 


PREFACE 

The  chief  interest  in  Secondary  School  science,  which 
for  a  long  time  was  concentrated  upon  the  later  years  of 
the  course,  has  recently  been  shifted  to  the  work  of  the 
first  year.  The  leading  reason  for  this  is  the  conviction, 
which  is  rapidly  becoming  general,  that  the  first  science 
of  the  High  School  should  be  fundamental  to  the  entire 
field  of  science  and  should  not  be  any  one  of  the  special 
sciences.  It  is  hard  to  see  how  Physiography,  Physiology, 
and  Biology,  the  usual  subjects  of  the  early  High  School 
years,  can  be  taught  satisfactorily  unless  the  pupil  has 
previously  acquired  the  elementary  physical  and  chemical 
conceptions  which  underlie  Physiography,  Physiology, 
and  Biology.  A  proof  that  this  need  is  felt  is  the  fact 
that  many  teachers  of  first-year  science,  no  matter  what 
their  subjects  may  be  called,  find  themselves  obliged, 
even  now,  to  give  a  large  part  of  their  class  time  to  the 
presentation  of  fundamental  physical  and  chemical  ideas. 

The  problem  involved  in  the  proper  preparation  of 
pupils  for  the  study  of  Physiography  and  the  biological 
sciences  cannot  be  solved  by  the  transfer  of  Physics  and 
Chemistry,  as  formal  subjects,  to  the  first  year  of  the 
High  School  curriculum.  The  cause  lies  both  in  the 
difficulty  of  the  subjects  themselves  and  also  in  the  high 
development  which  these  sciences  have  reached  in 
Secondary  Schools.  For  Physics  and  Chemistry  are 
now  taught  in  Secondary  Schools  in  a  way  and  with  an 

iii 


>•*  O  A 


iv  PREFACE 

equipment  far  in  advance  even  of  College  instruction  in 
these  subjects  a  generation  ago.  Work  of  this  character 
requires  a  certain  maturity  on  the  part  of  the  pupil,  as 
well  as  some  knowledge  of  other  High  School  subjects,  and 
it  cannot  be  maintained  unless  Physics  and  Chemistry 
are  kept  in  the  later  years  of  the  course. 

While  Physics  and  Chemistry  as  such  ought  not  to  be 
put  into  the  early  years  of  the  High  School,  yet  instruction 
in  the  simpler  principles  of  these  sciences  can  be  given 
in  a  first-year  General  Science  course.  The  most  im- 
portant part  of  this  course  will  be  introductory  notions  of 
physical  and  chemical  phenomena,  but  the  course  should 
include  much  more  than  this.  The  problems  of  modern 
conveniences  and  of  their  relation  to  scientific  discovery, 
the  soil  as  the  basis  of  agriculture,  plants  and  animals  and 
their  ascent  from  simpler  forms  to  those  that  are  more 
complex,  all  can  find  a  place  in  such  a  course.  So  can 
sanitation,  the  application  of  science  to  community  life. 

When  we  assign  to  General  Science  the  scope  suggested 
in  the  foregoing  paragraph,  the  need  of  it  in  the  first 
year  of  the  High  School  course  is  self-evident.  This  is 
true  even  if  we  confine  ourselves  to  the  staple  High  School 
curriculum  of  a  decade  ago.  But  when  we  remember 
that  this  curriculum  has  been  immeasurably  enlarged  by 
the  introduction  of  short  courses,  business  courses,  do- 
mestic science  courses,  agricultural  courses,  and  of  voca- 
tional guidance  in  all  courses,  the  demand  for  adequate 
first-year  science  instruction  becomes  imperative,  and 
the  argument  for  its  introduction  overwhelming.  The 
question  that  remains  is:  "Can  such  a  General  Science 
course  be  given  to  large,  first-year  High  School  classes, 


PREFACE  V 

with  their  varied  needs,  without  special  teachers  par- 
ticularly prepared  for  this  subject  and  without  expensive 
equipment  for  laboratory  work?"  The  answer  is  certainly 
"Yes."  To  give  the  answer  in  expanded  form  is  the 
purpose  of  this  book. 

The  "First  Year  of  Science"  is  written  to  meet  the 
need  of  General  Science  instruction.  It  consists  of  three 
parts:  the  text  proper,  the  laboratory  manual,  and  the 
Teacher's  Handbook.  The  text  and  laboratory  manual 
may  be  had  either  bound  together  or  in  separate  volumes. 
If  the  writer  were  asked  to  characterize  the  book  in  a 
phrase  or  two,  he  would  say  that  it  is  intended  to  stimu- 
late uncommon  thinking  about  common  things,  to  produce 
a  scientific  attitude  toward  everyday  problems,  to  give 
scientific  knowledge  to  as  large  a  body  of  our  people  as 
possible  in  order  that  modern  inventions  may  be  the 
tools  and  not  merely  the  toys  of  the  men  and  women  into 
whose  hands  they  are  placed. 

The  text  proper  consists  of  descriptive  matter,  of 
exercises,  and  of  chapter  summaries.  There  are  twenty 
chapters.  As  the  Table  of  Contents  shows,  about  half 
of  these  consist  of  elementary  Physics  and  Chemistry. 
The  chapters  on  Physics  contain  no  formulas  and  only  a 
few  simple  calculations;  there  are  no  symbols  or  equations 
in  the  chapters  on  Chemistry.  The  author's  plan  is  to 
give  only  the  primary  notions  of  matter,  force,  and  chem- 
ical action.  These  are  needed  for  all  subsequent  work 
in  pure  or  applied  science,  as  well  as  for  that  general 
knowledge  of  common  things  which  every  person  ought 
to  carry  away  from  a  High  School  course. 

In  the  latter  half  of  the  text  are' chapters  on  "Water, 


vi  PREFACE 

Heat,  Air,  and  Light  in  the  House,"  "The  Weather," 
" Rocks  and  Soil,"  "Plants,"  and  " Animals."  Chapters 
XVII  to  XX  are  given  to  elementary  Physiology  and 
Sanitation.  The  book  therefore  contains  the  material 
needed  by  schools  that  desire  to  give  a  short  course  in 
Physiology  at  the  end  of  the  first  year.  Coming,  as  it 
does,  after  the  elementary  Physics  and  Chemistry  of  the 
earlier  half  of  the  book,  and  immediately  after  the 
chapters  on  " Plants"  and  "Animate,"  the  work  in 
Physiology  ought  to  mean  far  more  to  the  pupil  than  if 
it  were  an  isolated  appendix  to  the  first  year's  work. 

The  illustrations  of  the  "First  Year  of  Science"  are 
unusually  numerous  and  especially  adapted  to  the  text. 
They  have  been  prepared  with  great  care,  for  they  are 
intended,  by  their  direct  appeal  to  the  eye,  to  enlarge 
materially  the  teaching  power  of  the  text.  To  this  end 
descriptive  matter  has  been  added  to  them  and  they 
have  been  made  very  simple.  The  parts  of  drawings 
have  usually  been  designated  by  names  rather  than  by 
letters. 

Exercises  are  given  at  the  end  of  each  chapter  and 
also  in  the  body  of  each  chapter  except  the  first.  The 
exercises  are  questions  taken  from  the  chapter;  they  en- 
courage the  pupil  to  apply  to  common  phenomena  what 
he  has  learned  in  the  text  and  the  laboratory  work. 

Summaries  are  placed  at  the  end  of  each  chapter  to 
bring  together  in  a  bird's-eye  view  the  leading  topics  of 
the  chapter. 

An  appendix  contains  useful  tables  and  a  reference 
Glossary  of  terms  used  in  the  book. 

The  laboratory   exercises   are   such   as   can   be  per- 


PREFACE  VII 

formed  with  simple  apparatus,  and  the  directions  are 
specific  both  as  to  the  form  of  apparatus  and  as  to  the 
quantity  of  materials  to  be  used.  A  special  feature  is  a 
series  of  alternative  experiments,  in  which  the  apparatus 
used  is  so  simple  that  it  can  be  made  at  home.  If  desired, 
most  of  these  alternative  experiments  may  be  performed 
by  the  pupil  at  home.  If  the  laboratory  facilities  of  the 
school  are  limited,  none  but  these  simple  experiments 
need  necessarily  be  used.  We  have  become  so  accus- 
tomed, in  our  well-equipped  schools,  to  laboratory  ap- 
paratus which  has  certain  definite  forms  and  requires 
certain  set  manipulations  that  we  are  likely  to  forget  that 
the  setting  up  of  home-made  apparatus  is  usually  far  more 
stimulating  to  the  pupil  than  even  the  best  of  ready- 
made  equipment.  Only  by  linking  our  science  with 
everyday  things  can  we  hope  to  convince  the  pupil  that 
science  is  only  common  sense  applied  to  daily  life. 

The  handbook  on  the  "  Teaching  of  First- Year  Science  " 
forms  the  third  part  of  the  book.  It  contains  material 
intended  chiefly  for  the  teacher's  use.  Here  are  dis- 
cussed the  topics  suitable  for  recitation  and  the  methods  of 
presenting  them,  the  amount  and  kind  of  work  to  be 
expected  of  pupils,  answers  to  exercises,  and  a  list  of 
experiments,  carefully  planned,  to  be  performed  by  the 
teacher  before,  or,  better,  with  the  class.  The  handbook 
is  designed  to  assist  the  teacher  in  every  possible  way  in 
making  the  elementary  science  course  profitable  and 
stimulating. 

In  the  preparation  of  this  book  the  writer  has  neces- 
sarily consulted  many  textbooks  of  Science,  and  put 
himself  under  deep  obligation  to  their  authors.  To  all  of 


Vlll  PREFACE 

these  he  desires  to  express  his  thanks.  He  is  especially 
grateful  to  his  friends,  Dr.  Eugene  C.  Woodruff,  of  Penn- 
sylvania State  College,  and  Miss  Marion  Sykes,  of  the 
Chicago  High  Schools,  for  valuable  criticisms  and  sug- 
gestions. 

The  author  desires  likewise  to  thank  the  many  in- 
dividuals and  firms  who  have  so  generously  assisted  him 
in  the  procuring  of  illustrations.  Among  these  are  Drs. 
O.  C.  Farrington  and  C.  F.  Millspaugh,  of  the  Field 
Museum  of  Natural  History,  Chicago;  the  International 
Stereograph  Co.,  Decatur  111.;  Dr.  S.  W.  Stratton,  of  the 
Bureau  of  Standards,  Washington;  Dr.  Orville  Wright, 
Dayton,  Ohio;  Mr.  William  D.  Richardson,  of  Swift  and 
Company;  Professor  Frederick  Starr,  of  the  University 
of  Chicago;  Professor  Martha  Van  Rensselaer,  of  the 
Department  of  Home  Economics,  Cornell  University;  and 
many  others  whose  names  appear  under  the  figures. 

The  drawings  for  the  illustrations  have  been  made  by 
Messrs.  William  F.  Henderson,  Macknet  Van  Deventer, 
Otto  Roth,  Alex.  Van  Praag,  Milford  Davis,  and  Leland 
Smith,  and  by  Miss  Hila  Ayres.  The  drawings  for  Figs. 
88,  206,  and  some  others  were  made  by  Miss  Ruth  Fuller. 
To  all  of  these  the  author  hereby  expresses  his  apprecia- 
tion and  gratitude.  J.  C.  H. 

Decatur,  Illinois. 


CONTENTS 

CHAPTER  I. 
Matter  and  Its  Measurement 1 

The  Earth  and  Science. —  Phenomena. —  The  Scientific  Way  or 
Method. —  Matter. —  Substances. —  How  We  Measure  Space  and 
Matter. —  Common  Units  of  Length. —  The  Metric  System. —  The 
Standard  Meter. —  Metric  Tables  of  Length,  Area,  and  Volume. — 
Larger  Units  of  Length. —  Weight. —  Units  of  Weight. —  Metric 
Units  of  Weight. —  Bureau  of  Standards. —  Summary. —  Exercises. 

CHAPTER  II. 
Force  and  Energy 17 

Gravity. —  Gravitation. —  Mass  and  Weight. —  Falling  Bodies. — 
Exercises. —  Force. —  Force  of  Expanding  Gases. —  Work  and  Energy. 
—  Power. —  Inertia  of  Matter. —  Flying  from  the  Center. —  Exer- 
cises.—  Cohesion  and  Adhesion. —  The  Surface  of  a  Liquid. —  Capil- 
lary Action. —  Density  and  Specific  Gravity. —  Buoyant  Force  of 
Liquids. —  Center  of  Mass  or  Gravity. —  Summary. —  Exercises. 

CHAPTER  III. 

Air  and  Fire 38 

The  Atmosphere. —  Weight  of  Air. —  Atmospheric  Pressure;  Ba- 
rometer —  Changes  in  Atmospheric  Pressure. —  Pumps. —  Compressed 
Air. —  Exercises. —  Collection  of  Gases. —  Discovery  of  Oxygen. — 
The  Air  a  Mixture. —  Burning  and  Oxidation. —  Flames. —  Prepara- 
tion of  Oxygen. —  Properties  of  Oxygen. —  Oxygen  and  Life. —  Exer- 
cises.—  How  Nitrogen  is  Prepared, —  Properties  of  Nitrogen. —  Nitro- 
gen and  Life. —  Liquid  Air. —  How  the  Atmosphere  is  Purified. — 
Summary. —  Exercises. 

CHAPTER  IV. 

Heat 59 

Heat  and  Matter.  Thermometers. —  The  Two  Thermometer 
Scales. —  Heat  and  Temperature. —  Ways  of  Distributing  Heat. — 
Radiation. —  Convection. —  Exercises. —  Physical  States  of  Matter; 
Solids. —  Liquids. —  Gases. —  Kindling  Temperature. —  The  Measur- 
ing of  Heat. —  Heat  and  Life. —  Clothing. —  Sources  of  Heat. —  Sum- 
mary.—  Exercises. 

ix 


X  CONTENTS 

CHAPTER  V. 

Water       . 76 

How  Water  Occurs  in  Nature. —  Substances  Dissolved  in  Natural 
Water. —  Drinking  Water. —  Hardness  of  Water. —  Purifying  Water. 
—  Filtering. —  Filtering  City  Water. —  Exercises. —  Why  Ice  Forms 
j  Only  at  the  Surface.—  Artificial  Ice.—  Steam.—  The  Boiling  Point 
Changes  with  Pressure. —  Solutions. —  Properties  of  Solutions.— 
Freezing  Mixtures.— Solubility. — Crystals. —  Summary. — Exercises. 

CHAPTER  VI. 

Elements  and  Compounds 94 

Physical  and  Cheniical  Changes.— Composition  of  Water. — 
Electrolysis  of  Water.— Elements  and  Compounds. —  Mixtures. — 
Preparation  of  Hydrogen. —  Properties  of  Hydrogen. —  Burning  of 
Hydrogen. —  Diffusion  of  Gases  and  Liquids. —  Exercises. —  Salt. — 
iSodium. —  Chlorine. —  Hydrochloric  Acid. —  Ammonia. —  Sulphur. — 
<.  Number  of  Elements  and  Compounds. —  Summary. —  Exercises. 

CHAPTER  VII. 
Carbon  and  its  Compounds       . .110 

Carbon  as  an  Element. —  Coal. —  Uses  of  the  Forms  of  Carbon. — 
Hydrocarbons. —  Petroleum. —  Flashing  Point. —  Other  Compounds 
of  Carbon. —  Dry  Distillation  of  Coal  and  Wood. —  Exercises. — 
Carbon  Dioxide. —  Carbon  Dioxide  in  the  Air. —  To  Prepare  Carbon 
Dioxide. —  Carbon  Dioxide  in  Fermentation. —  Baking  Powders. — 
Carbon  Dioxide  as  a  Fire  Extinguisher. —  Limestone. —  Summary. — 
Exercises. 

CHAPTER  VIII. 
Magnets  and  Electricity      .  (.  •    . .125 

Magnets. —  Poles  of  a  Magnet. —  Magnetic  Substances. —  The 
Magnetic  Field. —  The  Earth  a  Magnet. —  Exercises. —  Electric 
Charges  from  Friction. —  Conductors  and  Insulators. —  Attraction 
and  Repulsion.—  Induction  of  Charges. —  Electric  Discharge. —  Stor- 
ing a  Charge;  Leyden  Jar. —  Electricity  of  the  Atmosphere. — •  Light- 
ning Rods. —  Exercises. —  Electric  Currents. —  Kinds  of '  Cells. — Sal 
Ammoniac  Cell. —  Currents  and  Magnetism. —  Electro-Magnets. — 
The  Telegraph. —  Electric  Bell. —  Changing  the  Current  into  Light. — 
Electric  Furnaces. —  Electroplating. —  The  Dynamo. —  Electric  Mo- 
tor.—  Electric  Power. —  Summary. —  Exercises. 


CONTENTS  XL 

CHAPTER  IX. 

Light  and  Sound 150 

Luminous  Bodies. —  Transparent  and  Opaque  Bodies. —  Light  and 
Its  Properties. —  Images  through  Small  Openings. —  Shadows.— 
Brightness  or  Intensity  of  Light. —  Candle  Power. —  Exercises. — 
Division  of  Light  Striking  a  Body. —  Reflection  of  Light. —  Mirrors. — 
Dispersed  or  Diffused  Light. —  Refraction  of  Light. —  The  Lens. — 
Composition  of  White  Light. —  The  Rainbow. —  Absorption  of  Light; 
Color. —  The  Sky  and  Its  Colors. —  Change  of  Light  into  Heat. — 
Light  and  Life.—  Exercises. —  Simple  Microscope. —  Compound  Mi- 
croscope.—  The  Camera. —  How  Sounds  are  Made  and  Carried. — 
Sound  Waves. —  Echoes. —  Noise  and  Tone. —  The  Telephone. — 

Summary. —  Exercises. 

CHAPTER  X. 

Simple  Machines 174 

Need  of  Machines. —  Law  of  Machines. —  The  Lever. —  Classes  of 
Levers. —  Exercises. —  Pulleys. —  Wheel  and  Axle. —  Inclined  Plane. 

—  The  Wedge.— The  Screw.— Friction.— Sailboat.— The  Kite.— 
The  Airship. —  The  Windmill. —  Summary. —  Exercises. 

CHAPTER  XI. 

Acids,  Alkalies,  and  Cleaning 188 

Acids. —  Classes  of  Acids. —  Acids  and  Coloring  Matter. —  Action 
of  Acids  with  Metals. —  Action  of  Acids  with  Carbonates. —  Alkalies 
or  Bases. —  Caustic  Soda  and  Caustic  Potash. —  Neutralization; 
Salts. —  Tests  for  Certain  Salts. —  Exercises. —  The  Washing  of  Cloth- 
ing.—  Soap  and  Soap  Making. —  Action  of  Soap. —  Soap  and  Hard 
Water. —  Materials  of  Clothing. —  Dyes. —  Paints. —  Removal  of 
Stains. —  Summary. —  Exercises. 

CHAPTER  XII. 

Water,  Heat,  Air,  and  Light  in  the  House .  207 

Modern  Conveniences. —  Water  Supply. — •  Plumbing.—  Hydrants 
and  Traps. —  Kindling  a  Fire;  Matches. —  The  Fireplace. —  Stoves. — 
Gas  Stoves. —  Gasoline  Stoves. —  Electric  Stoves  and  Heaters. — 
Stream  and  Hot  Water  Heating. —  Thermostat. —  Exercises. —  Need 
of  Ventilation. —  Methods  of  Ventilation. —  Ventilation  without 
Fans. —  Need  of  Moisture  in  Air. —  Light  in  the  House.—  Glass. — 
Artificial  Lighting. —  Gas  for  Lighting. —  Incandescent  Mantles. — 
Gas  Pipes  and  Fixtures. —  The  Gas  Meter. —  Acetylene  for  Lighting. 

—  Electric  Lighting. —  The  Electric  Meter. —  Summary. —  Exercises. 


Xll  CONTENTS 

CHAPTER  XIII. 
The  Weather .      .  232 

Causes  of  Weather. —  Changes  in  Density  and  Pressure  of  Air. — 
Heating  of  the  Air. —  Moisture  of  the  Air. —  Humidity. —  Dew  and 
Frost. —  Fogs  and  Clouds. —  Forms  of  Clouds. —  Rain  and  Snow. — 
Hail. —  Rainfall. —  Exercises. —  The  Winds.—  Regular  Win  ds. — 
Storms  and  Cyclones. —  Thunderstorms. —  Tornadoes. —  Cyclones  of 
the  Tropics. —  Weather  Service. —  Weather  Maps. —  Summary. — 
Exercises. 

CHAPTER  XIV. 
Rocks  and  Soil    . 258 

The  Earth's  Crust. —  Some  Common  Rocks. —  Classes  of  Rocks. — 
Origin  of  Stratified  Rocks.  —  Origin  of  Igneous  and  Metamorphic 
Rocks. —  Weathering  of  Rocks. —  Causes  of  Weathering. —  Drift. — 
Erosion. —  Exercises. —  Soil. — •  Structure  of  Soil. — •  Tilling  the  Soil. 
—  Irrigation. —  Fertility. —  Loss  of  Fertility. —  Preserving  and  Re- 
storing Fertility. —  Rotation  of  Crops. —  Artificial  Fertilizers. — • 
Summary. —  Exercises. 

CHAPTER  XV. 

Plants        .   .  ,      .      ...      .      .      .      .     .;,  ' ,-,  -    .».,..     ...     .  282 

Plants  and  the  Soil. —  Functions  of  Plants. —  Germination  of  a 
Bean. —  Other  Seeds. —  Leaves. —  Work  of  Leaves. —  Modified 
Leaves. —  Stems. —  Structure  of  Stems;  Wood. —  Sap. —  Buds. — 
Roots. —  Underground  Storage  of  Food. —  Flowers. —  Formation  of 
Seeds. —  Dispersal  of  Seeds. —  Exercises. —  Classes  of  Plants. — 
Algae. —  Fungi. —  Mosses. —  Ferns. —  Seed  Plants. —  Economic 
Plants. —  Distribution  of  Plants. —  Summary. —  Exercises. 

CHAPTER  XVI. 

Animals     .      .      . .      .  312 

What  is  an  Animal? —  One-Celled  Animals. —  Simple  Many-Celled 
Animals. —  Starfishes. —  Worms. —  Mollusks. —  Crustaceans. —  In- 
sects.—  Exercises. —  Fishes. —  Amphibians. —  Reptiles. —  Birds. — 
Mammals. —  Importance  of  Animals  to  Man. —  Summary. —  Exer- 
cises. 


CONTENTS  Xlll 

CHAPTER  XVII. 

The  Human  Body  and  Its  Food 338 

Chief  Divisions  of  the  Body. —  Cells  and  Tissues  of  the  Body. — 
Structure  of  Bones. —  Joints. —  The  Skeleton. — •  Muscles  and  Tendons. 
—  Injuries  to  Bones  and  Muscles. —  Kinds  of  Food. —  Organs  of  Di- 
gestion; Glands.— The  Mouth.— The  Teeth.— The  Swallowing  of 
Food. —  Exercises. —  The  Stomach. —  Gastric  Juice. —  The  Intestines. 

—  The  Liver. —  The  Pancreas. —  Changes  in  Food  by  Digestion. — 
Absorption  and  Assimilation  of  Food. —  Storage  of  Food.—  Alcohol 
and  Its  Effects. —  Summary. —  Exercises. 

CHAPTER  XVIII. 

Circulation  and  Respiration 372 

Circulation  of  the  Blood. —  The  Heart. —  Arteries  and  Veins. — 
Capillaries. —  Blood. —  Lymph. —  Excretion. —  Respiration. —  The 
Lungs. —  Exchange  of  Gases  in  the  Lungs. —  Inspiration. —  Expira- 
tion.—  Exercises. —  The  Nostrils  and  Pharynx. —  The  Larynx  and 
Trachea. —  The  Voice. —  Speech. —  Care  of  the  Organs  of  Respiration. 

—  The  Skin. —  Perspiration. —  Hair  and  Nails. — •  Functions  of  the 
Skin. —  Summary. —  Exercises. 

CHAPTER    XIX. 

The  Nerves  and  the  Sense  Organs 395 

The  Nervous  System. —  Nerve  Cells  and  their  Structure. —  The 
Brain  and  its  Parts. —  Spinal  Cord. —  Sympathetic  System. —  Nervous 
System  as  a  Whole. —  Voluntary  and  Involuntary  Action. —  Reflex 
Action. —  Habit. —  Effect  of  Alcohol  and  Tobacco  on  the  Nerves. — 
Exercises. —  The  Special  Senses. — •  Touch. —  Taste. —  Smell. —  Hear- 
ing; Structure  of  the  Ear. —  Sight. — •  Eye  Socket  and  Lids. —  Parts  of 
the  Eye. —  Accommodaton. —  Near  and  Far  Sight. —  Summary. — 
Exercises. 

CHAPTER    XX. 

Sanitation 425 

Bacteria  and  their  Relation  to  Disease. —  How  the  Body  Resists 
Bacteria. —  Natural  Destruction  of  Germs. —  Artificial  Destruction 
of  Germs;  Antiseptics. —  The  Housefly  and  Mosquito  in  Relation  to 
Public  Health. —  Exposed  Food. —  Drinking  Fountains. —  Typhoid 
and  Sewage. —  Exercises. —  Tuberculosis  and  its  Cure. —  Spitting  in 
Public. —  Colds. —  Diphtheria. —  Antitoxins. — •  Smallpox. —  Vaccina- 
tion.—  Malaria  and  Yellow  Fever. —  Quarantine. —  Disinfection. — 
Summary. —  Exercises. 


THE  FIRST   YEAR  OF  SCIENCE 


CHAPTER  I 

MATTER  AND   ITS   MEASUREMENT 

1.  The  Earth  and  Science. —  In  order  that  we  may  get 
a  knowledge  of  the  earth  we  must  study  the  separate 
parts  that  make  it  up.  We  have  already  done  this  some- 
what in  Geography.  Hence  we  know  that  the  earth  con- 
sists of  many  different  rocks  and  soils,  trees  and  plants; 
of  bodies  and  streams  of  water;  of  the  air;  of  a  multitude 
of  animals  that  live  on  or  in  the  soil,  the  vegetation,  and 
the  water.  We  call  any  particular  rock,  tree,  lake,  or 
animal  an  object,  or  body.  The  sum  of  all  its  objects, 
large  and  small,  is  the  earth  itself.  Nature,  or  the  Uni- 
verse, includes  the  earth  together  with  the  sun,  moon, 
stars,  etc. 

Science  is  the  study  of  the  truth  about  the  objects  of 
nature.  Since  the  number  of  objects  is  very  large,  one 
method  of  studying  nature  is  to  find  important  resem- 
blances and  differences  between  objects.  We  can  then 
arrange  objects  in  groups  or  classes.  Thus,  we  can  make 
a  division  of  all  objects  into  (a)  living  objects  and  (6) 
non-living  objects.  Living  things  may  then  be  classified 
as  either  animals  or  plants.  Plants  in  their  turn  may  be 

i 


"/ 

2  MATTER  AND  ITS  MEASUREMENT 

grouped  as  flowering  or  non-flowering  plants,  and  each  of 
these  will  have  many  divisions.  To  take  one  illustration : 
the  daisy,  the  dandelion,  and  the  sunflower  belong  in  one 
great  group  of  flowering  plants  because  the  structure  of 
their  flowers  is  similar,  while  the  rose,  the  strawberry, 
and  the  apple  belong  in  an  entirely  different  group. 

But  the  classifying  of  objects,  while  very  valuable,  is 
only  a  part  of  science.  By  far  the  greater  part  is  taken  up 
with  the  study  of  the  objects  themselves.  We  want  to 
know  their  beginning,  or  origin,  what  they  do,  and  what 
becomes  of  them.  For  the  objects  of  nature  are  always 
changing.  Living  things  grow,  and  then  decay;  rocks 
are  made,  and  then  crumble.  Even  the  "eternal  hills" 
are  worn  away,  and  the  "fixed"  stars  appear  to  be  fixed 
only  because,  to  the  eye,  they  change  their  positions  so 
slowly. 

2.  Phenomena. —  By  a  "phenomenon"  (plural,  phe- 
nomena) we  mean  simply  a  happening,  a  change,  that  takes 
place  in  some  object.  It  is  not  necessarily  a  strange 
occurrence,  like  the  appearing  of  a  comet  or  an  eclipse. 
We  observe  a  phenomenon  when  we  see  a  marble  roll  over 
the  floor,  when  an  apple  falls  to  the  ground,  when  a  com- 
pass needle  takes  a  north  and  south  position,  when  an 
electric  light  is  "turned  on"  or  "goes  out."  Other  phe- 
nomena are  such  common  changes  as  the  burning  of  wood, 
the  souring  of  milk,  the  freezing  of  water,  and  the  rusting 
of  iron. 

*  3.  The  Scientific  Way,  or  Method. —  Primitive  man 
probably  reasoned  in  a  very  childish  way  about  objects 


THE  SCIENTIFIC  WAY  £ 

and  phenomena.  We  know  that  men  were  once  satisfied 
to  explain  an  eclipse  of  the  sun  (cf.  §  169)  by  saying  that 
it  was  caused  by  a  great  dragon,  or  bird,  or  spirit,  passing 
across  the  sky.  Even  in  comparatively  recent  times 
people  have  had  ideas  only  a  little  better,  for  when  Colum- 
bus asserted  that  the  earth  was  a  sphere  the  men  of  his 
day  ridiculed  him.  They  were  sure  that  if  the  earth  were 
round,  the  people  on  the  other  side  of  the  earth  must  be 
standing  on  their  heads. 

But  men  interested  in  finding  out  about  nature  have 
kept  on  experimenting  and  reasoning,  until  they  have 
come  to  understand  something  of  nature's  ways.  They 
have  made  the  most  progress  when  they  have  used  the 
method  of  study  which  we  now  call  the  scientific  method. 
This  method  consists  in  — 

(a)  getting  together  as  many  facts  as  possible  regard- 
ing the  object  or  phenomenon  studied; 

(b)  arranging  these  facts  in  the  order  of  their  impor- 
tance; 

(c)  drawing  some  conclusion. 

Men  now  use  the  scientific  method  to  get  at  every  sort 
of  knowledge,  even  the  knowledge  needed  to  conduct  a 
business  or  to  "keep  house." 

We  may,  therefore,  define  science  a  second  time  and  say  that  it  is 
organized  knowledge.  We  call  such  knowledge  "organized"  because, 
like  a  plant  or  animal,  it  is  composed  of  parts  —  called,  in  the  plant  or 
animal,  organs  —  each  of  which  has  a  particular  place  and  a  particular 
duty. 

General  Science,  which  we  are  now  to  study,  takes  up  many  topics 
also  found  in  the  special  sciences,  such  as  Physics,  Chemistry,  Botany, 
Physiology,  etc.  A  knowledge  of  these  topics  is  necessary  not  only  to 
the  students  who  are  later  to  study  the  special  sciences,  but  to  every 


MATTER  AND  ITS  MEASUREMENT 


FIG.  1. 
Flask  with 
a  glass-stop- 
pered tube. 


one  who  wants  to  understand  and  to  use  scientific  methods  and 
apparatus  in  the  home,  in  the  shop  or  store,  on  the  farm — in  short, 
anywhere  in  his  daily  life. 

4.  Matter. —  Suppose  we  examine  a  number  of  objects, 

such  as  pieces  of  marble,  sulphur,  wood,  lead,  etc.  They 
are  certainly  unlike  in  color,  size,  and  shape. 
Are  they  alike  in  any  particulars?  In  the  first 
place,  they  all  take  up  room,  or  occupy  space. 
We  cannot  think  of  a  body  that  does  not.  A 
second  way  in  which  objects  are  alike  is  that  all 
of  them  have  weight  (cf.  §  20).  We  accept  these 
statements  readily  when  we  think  of  lead,  of 
marble,  of  water,  of  rock.  These  are  solids  or 
liquids,  and  are  readily  seen  and  handled.  But 
even  invisible  gases,  like  the  air,  take  up  room 
and  have  weight,  just  as  solid  and  liquid  objects 

do.    A  vessel,  such  as  a  flask  (Fig.  1), 

from  which  the  air  may  be  removed,  is 

lighter  when  empty  than  when  full  of  air. 

Again,  a  vessel  full  of  air  cannot  be  filled 

with  water  unless  the  air  is  allowed  to 

escape.    We  see  this  when  we  try  to  pour 

water  rapidly  into  a  narrow-mouth  bottle; 

the  water  can  enter  only  a  little  at  a  time, 

as  bubbles  of  air  come  out  to  make  room 

for  it.    Another  illustration  is  seen  in  the 

construction  of  a  kerosene  can  (Fig.  2).    The  can  has 

an  opening  at  the  top  not  only  to  allow  the  can  to  be 

filled  with  kerosene,  but  also  to  permit  air  to  enter  in 

a  steady  stream  as  the  kerosene  is  poured  out  of  the 

spout. 


FIG.  2. 

As  kerosene  comes  out 
air  enters. 


SUBSTANCES  5 

Now,  why  do  all  bodies  occupy  space?  We  answer  by 
saying  that  bodies  are  portions  of  matter,  and  that  matter 
occupies  space.  Matter  not  only  occupies  space,  but  it  has 
weight.  When  we  give  the  weight  of  an  object  we  give 
the  weight  of  the  matter  in  it. 

5.  Substances. —  While  it  is  important  for  us  to  get 
the  general  idea  of  matter,  yet  we  always  observe  and 
study  matter  in  separate  portions,  or  bodies  (cf.  §  1). 
Each  body  may  be  made  up  of  one  kind  of  matter  or  of 
several  kinds.  Thus,  we  might  have  chips  of  marble, 
each  consisting  of  one  kind  of  matter  (marble),  or  we 
might  have  chips  consisting  of  a  mixture  of  marble  and 
clay.  The  kinds  of  matter  are  called  substances.  The 
qualities,  or  characteristics,  of  a  body  depend  upon  the 
qualities  of  the  substance  or  substances  of  which  it  is 
composed.  The  qualities  of  a  substance  are  called  its 
properties.  We  learn  the  properties  of  any  given  sub- 
stance by  the  use  of  our  senses  or  by  experiment. 

Some  illustrations  will  make  clear  the  meaning  of  properties  and  the 
difference  between  bodies  and  substances.  A  lake  is  a  body  of  water; 
water  is  not  a  body  but  a  kind  of  matter,  that  is,  a  substance.  A  pencil 
is  a  body  consisting  of  the  substances  wood  and  "black  lead,"  or 
graphite  (cf.  §  117).  We  can  readily  tell  the  wood  from  the  graphite 
by  the  properties  of  each.  Thus,  the  wood  is  soft  when  cut;  it  is  brittle, 
light  in  color,  and  it  floats  upon  water;  it  burns  when  heated  in  the  air. 
Graphite,  on  the  other  hand,  has  different  properties.  It  too  is  brittle, 
but  its  color  is  black,  it  sinks  in  water,  burns  with  great  difficulty,  and 
leaves  a  black  mark  when  rubbed  on  paper.  All  these  properties  dis- 
tinguish graphite  from  wood. 

Sulphur,  or  "brimstone,"  is  another  common  substance.  It  is  dis- 
tinguished from  wood  and  from  graphite  by  the  following  properties: 


6  MATTER  AND  ITS  MEASUREMENT 

it  is  yellow,  crystalline  (Fig.  3),  brittle;  it  sinks  in  water,  and  does  not 
dissolve  in  water;  it  melts  when  heated,  giving  a  clear,  yellow  liquid; 
it  burns  readily  in  the  air  (cf.  §  51).  Wood 
tipped  with  sulphur,  phosphorus,  and  some  other 
substances  makes  up  another  body,  a  match 
(cf.  §  72).  Now,  the  properties  of  the  substances 
FIQ  3  composing  a  match  make  the  uses  of  the  match 

A  Sulphur  Crystal.        quite  different  from  the  uses  of  a  pencil. 

General  and  Special  Properties. —  We  must  remember 
that  the  properties  of  a  body,  such  as  its  filling  space,  hav- 
ing weight,  etc.,  are  the  general  properties  of  all  matter, 
and  do  not  belong  to  one  substance  more  than  to  another. 
The  special,  or  specific,  properties  of  a  substance  belong 
to  that  substance  alone.  No  two  substances  have  exactly 
the  same  special  properties. 

6.  How  We  Measure  Space  and  Matter. —  We  know 
from  experience  that  all  bodies  have  three  dimensions; 
namely,  length,  breadth,  and  thickness.  We  also  think  of 
space  as  having  these  dimensions.  When  we  say  that  a 
body  has  a  definite  volume,  we  mean  that  it  fills  a  definite 
amount  of  space.  We  do  not  know  what  space  is,  but  we 
distinguish  between  space  and  matter, 
calling  that  " space"  which  is  not  filled 
with  some  object.  On  the  earth,  a  por- 
tion of  space  from  which  matter  has 
been  removed  is  called  a  vacuum.  As 
already  stated  (cf.  §  4),  air  and  other 
gases  are  matter,  not  space.  FlG  4 

If  a  body  is  regular  in  shape,  we  can 
readily  calculate  its  volume.    Thus,  we  obtain  the  vol- 
ume of  a  cube  (Fig.  4)  from  the  formula, 


THE  METRIC  SYSTEM 


Volume  =  length  X  breadth  X  thickness. 

We  can  get  the  volume  of  an  irregular  solid  by  im- 
mersing it  in  some  liquid  (Fig.  5).  The  body  displaces 
its  own  volume  of  liquid. 


The  boundaries  of  a  body,  by  which  the  mat- 
ter of  the  body  is  separated  from  other  matter, 
or  from  space,  are  called  surfaces.  A  cube  has 
six  plane  surfaces.  A  sphere  has  a  uniformly 
curved  surface.  A  surface  has  two  dimensions, 
length  and  breadth.  The  boundaries  of  a  sur- 
face are  lines,  with  only  the  dimension  of  length. 


—50 
—40 


,, 


FIG.  5. 


7.  Common  Units  of  Length. —  The 

unit  of  length  used  in  Great  Britain 
and  the  United  States  is  the  yard.  Originally  the  yard 
was  probably  the  length  of  the  King's  arm,  but  this 
changeable  standard  has  become  fixed,  and  is  now  the 
length  of  a  standard  metal  bar  kept  in  London,  with  a 
copy  at  Washington.  The  foot  was  originally  the  length 
of  the  human  foot,  but  became  fixed  as  ^  of  a  yard. 
The  inch  was  fixed  as  ^  of  a  foot. 

8.  The  Metric  System. —  The  yard  and  its  subdivisions 
and  multiples  are  still  used  for  ordinary  measurements 
in  this  country  and  England,  but  on  the  continent  of 
Europe  a  different  system  prevails.     This  is  called  the 
metric  system,  from  its  standard,  the  meter.     It  is  a 
decimal  system,  and  has  been  adopted  by  scientific  writers 
the  world  over.    The  coinage  of  this  country  has  long  been 
upon  the  decimal  basis,  and  the  names  used  for  subdivi- 
sions of  the  dollar  are  also  used  for  subdivisions  of  the 


8  MATTER  AND  ITS  MEASUREMENT 

meter.  The  name  of  the  smallest  money  unit,  the  mill, 
is  derived  from  the  Latin  millia,  meaning  1000.  Cent  is 
from  centum,  or  100,  and  dime  is  from  decem,  meaning  10. 
A  mill  is  iffio  of  a  dollar;  a  cent  is  150 ;  a  dime,  A.  In 
the  same  way  1^5  of  a  meter  is  called  a  millimeter ;  n^, 
a  centimeter;  and  ^,  a  decimeter. 

9.  The  Standard  Meter. —  Men  intended  that  the  meter 
should  be  40,000.000  of  the  earth's  circumference,  but 
we  now  define  it  as  the  distance  between  two  fine  lines 

ruled   on   a    metal    bar 
(Fig.  6).    The  bar  is 
made  of  an  alloy  (mix- 
united  StatefproLype  Meter.  tui>e)  °f  tn^  metals  pldtl- 

num  and  indium.    While 

the  distance  between  the  lines  is  being  measured,  the 
bar  is  kept  at  the  temperature  of  melting  ice;  that  is, 
at  0°  Centigrade  (cf.  §§63  and  69).  Thirty-one  inter- 
national standard  meters  were  made  at  Paris  and  dis- 


D             1              23456 

1  1  ii  1  1  II  1  i  M  I  In  1  1  1  1  II  1  1  1  ii  I   1  1  1  1   M   1  1  1  1  M  li  1  1  il  in  i  II  1  1  1  1 

7             8    C 

1    1  1  1  1    II    1  1    1  II  II  11  1 

.M 

1  i  '  j  '  i  '  1  '  |  '  |  '  i  '  1  '  i  •  |  '     •     •  i  '  |  '  i  •     •  i  •     •  i  • 

D                                   I                                   2 
FIG.  7. 
Inches  and  Centimeters. 

1  •  |  •      •      '   1   <  |   '   1   ' 

3          IN. 

tributed  among  the  principal  governments  of  the  world. 
Two  of  them  were  brought  to  the  United  States  and  are 
kept  at  Washington. 

The  length  of  the  meter  is  39.37  inches,  or  3.28  feet.  The  exact 
measurement  of  the  meter  is  very  difficult,  because  the  metal  bar 
changes  its  length  slightly,  but  in  recent  years  the  meter  has  been  made 


LARGER  UNITS  OF  LENGTH  9 

equal  to  the  length  of  a  certain  number  of  light-waves  (cf.  §  179),  so 
that  if  all  the  standard  meters  were  destroyed,  a  new,  perfect  meter 
could  be  obtained. 

10.  Metric  Tables  of  Length,  Area,  and  Volume. — 

The  metric  table  of  length  (Fig.  7)  is — 

10  millimeters  (mm.)  =  1  centimeter. 
10  centimeters  (cm.)  =  1  decimeter. 
10  decimeters  (dm.)   =  1  meter. 
1000  meters  (m.)  =  1  kilometer. 

1  kilometer  (km.)     =0.6214  mile. 

For  surface  measure  the  table  is  — 

100  square  millimeters  =  1  square  centimeter. 
100  square  centimeters  =  1  square  decimeter. 
100  square  decimeters  =  1  square  meter. 

For  cubic  measure  the  table  is  - 

1000  cubic  millimeters  (c.  mm.)  =  1  cubic  centimeter. 

1000  cubic  centimeters  (c.c.  or  c.cm.)  =  1  cubic  decimeter. 
1000  cubic  decimeters  (c.  dm.)  =  1  cubic  meter. 

One  cubic  decimeter  is  called  a  liter  (pronounced  leter). 
It  is  a  little  larger  than  a  U.  S.  liquid  quart.  As  the  last 
table  shows,  the  cubic  decimeter,  and  therefore  the  liter, 
contains  1000  cubic  centimeters.  The  relation  between 
metric  units  and  other  ordinary  units  is  shown  in  the 
Appendix,  Table  II. 

11.  Larger  Units  of  Length. —  For  distances  on  the  earth  the  mile 
(5,280  feet)  and  the  kilometer  (3,281  feet)  are  convenient  units.  But 
when  we  express,  in  miles,  the  distance  of  the  earth  from  the  sun,  the 


10 


MATTER  AND  ITS  MEASUREMENT 


/* 


FIG.  8. 

The  Big  Dipper  and  the  North  Star 
on  September  22,  8  p.  m. 


number  —  about  93,000,000  —  is  so  large  that  it  means  very  little  to 
us.  We  can  get  a  better  idea  of  the  distance  by  saying  that  it  takes 
over  eight  minutes  (499  seconds)  for  the  sun's  light  to  reach  us,  al- 
,  though  light  travels  at  the  rate  of  about 
186,000  miles  (300,000  kilometers)  each 
second.  Or  we  may  say  that  a  train 
traveling  a  mile  a  minute  would  need 
about  178  years  to  get  to  the  sun.  Yet 
the  earth's  distance  from  the  sun  is  very 
small  as  compared  with  its  distance  from 
the  stars.  The  light  of  the  nearest  fixed 
star  requires  about  4  years  to  reach  the 
earth;  while  the  light  of  Polaris,  the 
" North  Star"  (Fig.  8),  that  enters  our 
eyes  to-night  left  the  star  about  47  years 
ago.  In  order  to  avoid  the  use  of  the 
many  figures  needed  to  express  such 
enormous  distances  in  miles  astronomers  use  a  larger  unit  for  star 
distances.  This  unit  is  the  light-year;  that  is,  the  distance  which 
light  travels  in  a  year.  The  light-year  is  about  63,000  times  as  great 
as  the  distance  of  the  earth  from  the 
sun,  or  63,000X93,000,000  miles. 

12.  Weight. — Just  as  we  might 
estimate  moderate  distances  by 
means  of  our ' '  sense  of  distance/' 
or  "  sense  of  space,"  so  we  might 
get  the  weights  of  many  objects 
by  using  our  " sense  of  weight." 
In  fact,  the  experienced  cashier 
and  baggageman  often  develop 

the  sense  of  weight  to  a  remarkable  degree,  owing  to 
years  of  training  in  the  "hefting"  of  coins  and  trunks, 
respectively.  However,  to  get  distances  accurately  we 


FIG.  9. 

The  Chemical  Balance. 


UNITS  OF  WEIGHT 


11 


FIG.  10. 
Trip  Scale. 


use   measuring   rods,    tapes,    chains,    etc.,    and   to   get 
accurate  weights  we  use  balances  and  scales. 

If  the  balance  has  two  arms  of  equal  length,  as  in 
the  chemical  balance  (Fig.  9)  and 
the  "trip"  balance  of  the  labora- 
tory (Fig.  10),  the  weights  used  as 
the  counterpoise  must  be  exactly  as 
heavy  as  the  object  weighed.  The 

object  to  be  weighed  on 

such  balances  is  placed  in 

the  left-hand  pan,  and  the  weights  in  the  right. 

In  making  the  spring  balance  (Fig.  11)  the  manufac- 
turers stretch  the  spring  by  means  of  weights  placed  on 
the  hook,  and  then  mark  the  successive  positions  of  the 
pointer  on  the  graduated  scale.    A  body  which  stretches 
FIG.  11.        the  spring  to  the  same  extent  must  be  just  as  heavy  as 
the  weights  used.    Scales  for  weighing  heavy  objects, 
such  as  cars,  or  loads  of  hay  or  coal,  are  made  by  putting  together  a 
system  of  levers  (cf.  §  198),  so  that  the  whole  apparatus  can  be  kept 
in  a  small  space  under  the  weighing  platform. 


13.  Units  of  Weight. —  Man  has  used  many  units  of 
weight.  The  old  English  pound  (from  the  Latin  pondus, 
a  weight)  was  originally  the  weight  of  7680  grains  of  wheat 
"all  taken  from  the  middle  of  the  ear,  and  well  dried." 
From  this  origin  of  the  pound  came  the  word  "grain," 
the  small  division  of  the  pound.  Henry  VIII,  King  of 
England  from  1509  to  1547,  made  the  "avoirdupois" 
pound  the  unit  of  weight.  It  contains  16  ounces,  or  7000 
grains.  In  1758  a  piece  of  brass  of  suitable  size  was  de- 
clared by  Parliament  to  be  a  pound.  Later,  a  piece  of 


12 


MATTER  AND  ITS  MEASUREMENT 


platinum  was  substituted  for  the  brass.  The  English 
pound  weight  is  still  this  platinum  standard  pound. 
Copies  of  it,  also  of  platinum,  are  kept  in  the  United 
States  (Washington)  and  in  other  countries. 


The  abbreviation  "lb.,"  for  "pound,"  comes  from  the  Latin  libra, 
or  scales.  The  word  "ounce"  is  probably  from  unus,  "one,"  and  was 
originally  applied  to  &  of  a  pound,  as  it  still  is  in  "Troy  "  weight.  In 
the  form  "inch"  it  was  also  applied  to  1*3  of  a  foot.  The  ton  probably 

received  its  name  from  the  "tun,"  a 
large  cask  that  held  about  2,000  pounds 
of  water. 

14.  Metric  Units  of  Weight- 
In  the  metric  system  the  com- 
mon weight  units  are  the  gram 
and  kilogram  (1000  grams).  A 
liter  of  pure  water  at  4°  C.  (cf.  § 
87)  weighs  one  kilogram.  This 
is  abbreviated  to  "kilo"  or  to 
1  i  kg. ' '  The  international  stand- 
ard kilogram  is  a  piece  of  plati- 
num, as  is  the  English  standard 
pound.  Forty  of  these  were  constructed  in  Paris,  and 
two  of  them  are  in  the  Bureau  of  Standards,  at  Wash- 
ington (Fig.  12). 


FIG.  12. 
The  Standard  Kilogram. 


One  cubic  centimeter  of  water,  that  is,  i^bo  of  a  liter, 
weighs  one  gram. 


Subdivisions  of  the  gram,  like  those  of  the  meter,  are  formed  from 
the  prefixes  "milli,"  "centi,"  and  "ded." 


BUREAU  OF  STANDARDS  13 

10  milligrams  (ing.)  =  1  centigram. 
10  centigrams  (eg.)   =  1  decigram. 
10  decigrams  (dg.)    =  1  gram. 
1000  grams  (g.)  =  1  kilogram. 

1  kilogram  (kg.)      =  2.2046  Ibs. 
1000  kilograms  =  1  metric  ton. 

Two  advantages  which  the  metric  system  has  over  the  English  sys- 
tem are: 

(1)  It  is  a  decimal  system. 

(2)  It  is  already  in  use  in  practically  all  of  Europe,  and  in  Latin 
America. 

Just  as  we  can  gather  together  "one  dollar,  four  dimes,  and  three 
cents"  into  the  expression  "$1.43,"  so  we  can  write  "two  grams, 
five  decigrams,  three  centigrams,  and  one  milligram"  as  "2.531  g." 
A  weight  consisting  of  several  English  units,  such  as  two  pounds,  six 
ounces,  and  fifteen  grains,  cannot  be  expressed  in  pounds  without 
much  calculation. 

15.  Bureau  of  Standards. —  Since  it  is  important  that 
all  apparatus  used  for  measuring  shall  be  correct,  several 
governments  have  established  "Bureaus  of  Standards/' 
to  which  such  apparatus  may  be  sent  for  the  purpose  of 
comparing  it  with  the  standard  apparatus  of  the  govern- 
ment. The  United  States  Bureau  of  Standards  (Fig.  13) 
was  established  at  Washington  in  1901. 

Originally  the  Bureau  was  only  a  place  for  keeping  the  pound,  yard, 
gallon,  bushel,  meter,  kilogram,  etc.,  up  to  standard,  but  it  has  grown 
to  be  much  more  than  this.  The  many  new  industries  that  have 
arisen  in  recent  years  and  the  application  of  scientific  methods  to  old 
industries  make  new  standards  necessary.  It  is  also  important  that 
both  the  quantities  of  the  materials  that  go  into  manufactured  articles, 
as  well  as  their  qualities,  or  properties  (cf.  §  5),  shall  be  definitely 
known.  Hence  the  Bureau  furnishes  standards  of  measurement  for 
electricity,  the  unit  of  light  intensity  (known  as  the  "candle  power"; 


14  MATTER  AND  ITS  MEASUREMENT 

cf.  §  171),  standard  thermometers  for  determining  temperature  (c/. 
§  63),  and  standard  pyrometers  for  determining  higher  temperatures 
than  the  thermometer  will  measure.  We  can  realize  the  value  of  this 
work  when  we  understand  that  the  measurement  of  high  temperatures, 
for  example,  is  necessary  in  such  important  industries  as  making  glass, 


FIG.  13. 
The  Bureau  of  Standards. 

pottery,  and  illuminating  gas,  and  in  the  preparation  and  working  of 
the  metals.  Besides,  the  Bureau  determines  the  strength  of  materials 
such  as  wood,  steel,  and  cement,  the  fuel  value  of  coal,  petroleum,  etc., 
as  well  as  many  other  properties  which  the  modern  manufacturer 
needs  to  know. 

16.  Summary. —  Science  is  organized  knowledge.  It  arranges  ob- 
jects into  groups  or  classes  and  studies  the  changes  that  objects 
undergo. 


SUMMARY  15 

The  scientific  method  is  necessary  in  everyday  life  quite  as  much 
as  in  study  and  investigation. 

Phenomena  are  the  changes  in  objects. 

Objects  are  portions  of  matter. 

Matter  exists  in  the  solid,  the  liquid,  and  the  gaseous  form. 

Matter  occupies  space  and  has  weight. 

Substances  are  the  kinds  of  matter. 

Properties  are  the  qualities  by  which  we  distinguish  one  substance 
from  another. 

Space  is  that  which  contains  no  matter. 

A  space  from  which  the  matter  has  been  removed  is  called  a  vacuum. 

Matter  has  three  dimensions:  length,  breadth,  and  thickness. 

The  meter  is  the  unit  of  the  metric  system.    It  contains  39.37  inches.. 

The  kilometer  is  0.6214  miles. 

The  liter  is  the  unit  of  volume.  It  equals  1  cubic  decimeter,  or 
1.0567  U.  S.  liquid  quarts. 

The  standard  pound  weight  contains  16  ounces,  or  7000  grains. 

The  gram  is  the  weight  of  1  cubic  centimeter  of  pure  water  at  4°  C. 

The  kilogram  is  1000  grams.  It  is  the  weight  of  one  liter  of  pure 
water,  and  equals  2.2046  pounds. 

The  Bureau  of  Standards  keeps  the  standard  weights  and  measures, 
compares  common  weights  and  measures  with  the  standard  ones,  makes 
new  standards  as  new  industries  demand  them,  and  determines  the 
properties  of  materials. 

17.  Exercises. 

1.  Name  the  so-called  "five  senses."     Are  there  any  senses  besides 
these?    Explain. 

2.  Name  two  substances  that  you  can  distinguish  from  each  other 
by  each  of  the  five  senses.     For  ' '  hearing,"  think  of  the  way  we  test  the 
genuineness  of  a  coin.  * 

3.  Make  a  list  of  ten  objects,  and  write  opposite  each  the  substance 
or  substances  of  which  it  is  made  up. 

4.  Make  a  list  of  all  the  properties  you  can  think  of  for  each  of  the 
following  substances:  iron,  water,  sugar,  wood,  and  coal. 


16  MATTER  AND  ITS  MEASUREMENT 

5.  Name  five  phenomena  besides  those  of  §  2. 

6.  Compare  the  way  in  which  water  is  poured  out  of  an  inverted, 
small-mouth  bottle  with  the  way  in  which  it  is  poured  out  of  a  pitcher. 
Explain. 

7.  Find  the  number  of  cubic  feet  of  air  in  a  room  14  ft.  by  14  ft.  by 
9  ft.  high.    Find  the  weight  of  the  air  in  ounces,  if  one  cubic  foot  of  air 
weighs  1%  ounces.    Reduce  the  weight  to  pounds. 

8.  Write  down  as  grams  and  decimal  parts  of  a  gram  6  grams,  5 
decigrams,  3  centigrams,  and  9  milligrams.    Subtract  from  this  number 
the  sum  of  2  grams  and  8  centigrams. 

9.  Locate  the  North  Star  to-night  or  the  next  clear  night,  note  the 
hour,  and  draw  a  diagram  to  show  the  position  of  the  "Big  Dipper" 
with  reference  to  the  star.   What  stars  of  the  dipper  are  the ' '  Pointers' '  ? 

10.  Look  up  (in  the  Glossary  at  the  back  of  this  book)  the  difference 
between  planets  and  fixed  stars.    Name  some  of  the  planets.    Name 
some  fixed  stars  besides  Polaris. 

11.  Look  up  the  distance  of  the  moon  from  the  earth.    What  is  the 
moon's  diameter?   The  earth's? 

12.  Look  in  a  dictionary  for  the  origin  of  the  words  quart,  gram, 
meter,  vacuum,  and  substance. 

13.  What  are  the  proofs  that  the  earth  is  sphere-like  and  not  flat? 

14.  Name  some  scientific  methods  or  apparatus  that  have  recently 
been  brought  into  our  homes.    Into  factories.    Into  stores.    Name 
some  that  are  used  on  the  farm.    In  navigation. 


CHAPTER  II 

FORCE  AND  ENERGY 

18.  Gravity. —  Many  of  our  most  common  phenomena 
are  simply  changes  in  the  position  of  bodies.  The  falling 
of  an  apple,  the  movement  of  water  in  waves  and  tides, 
the  flight  of  a  stone  or  a  bullet  through  the  air,  all  illustrate 
this.  So  do  the  turning  of  a  magnetic  needle  toward  the 
poles  and  the  vibrating  of  a  violin  string.  Now,  why 
does  a  stone  or  an  apple  "fall"?  Sir  Isaac  Newton  gave 
the  reason  when  he  said  that  the  earth  pulls  the  apple 
and  all  other  falling  bodies.  We  do  not  find  it  easy  to 
picture  to  ourselves  just  how  the  earth's  ' '  pull "  is  applied. 
A  horse  pulling  a  wagon  is  attached  to  the  wagon,  and  the 
strength  of  his  muscles  overcomes  the  tendency  of  the 
wagon  to  remain  at  rest.  Similarly,  an  engine  is  attached 
to  the  cars  it  pulls.  But  the  earth's  attraction  acts 
through  space,  without  visible  or  invisible  attachment. 

We  can  illustrate  the  earth's  attraction,  on  a  small  scale,  by  the 
action  of  a  magnet  upon  an  iron  nail.  The  magnet  is  a  piece  of  steel 
which  has  been  "magnetized,"  so  that  it  has  the  power  of  drawing  to 
itself  bodies  consisting  of  steel,  iron,  nickel,  etc.  There  is  no  connection 
between  the  magnet  and  the  attracted  object,  yet  we  know  that  there 
is  action  between  them. 

It  is  just  as  necessary  for  us  to  assume  that  the  apple 
attracts  the  earth  as  that  the  earth  attracts  the  apple. 
It  is  also  just  as  reasonable  to  suppose  that  the  earth  falls 

17 


18 


FORCE  AND  ENERGY 


toward  the  apple  as  that  the  apple  falls  toward  the  earth. 
But  the  distance  that  the  earth  moves  before  they  meet 
must,  of  course,  be  very  small,  owing  to  the  much  greater 
size  of  the  earth.  This  earth-pull  we  call  gravity. 

19.  Gravitation. —  The    attraction    which    exists    be- 
tween the  earth  and  bodies  near  its  surface  exists  also 

„  between  all  bodies  of  matter  on  the  earth 
and  between  the  earth  and  the  sun,  moon, 
and  other  heavenly  bodies.  It  is  called  gravi- 
tation. Gravity  is  merely  a  particular  case 
of  gravitation. 

The  gravitation,  or  attraction,  between  two 
bodies  on  the  earth,  as,  for  example,  between 
two  suspended  balls  (Fig.  14),  is  not  easily 
observed,  because  the  great  attraction  of  the 
earth  for  both  of  them  holds  them  in  a  ver- 
tical position.  By  means  of  a  celebrated 
experiment  first  carried  out  in  the  latter  part 
of  the  18th  century  this  attraction  was  made 
visible.  A  large  ball  of  lead  and  a  small  one 
of  copper  were  suspended  side  by  side,  with 

the  result  that  the  copper  ball  was  drawn  aside  from  a 

vertical  position. 

20.  Mass  and  Weight. —  We  need  to  distinguish  be- 
tween the  mass  of  a  body  and  the  weight  of  a  body.    New- 
ton saw  that  the  earth's  attraction  for  a  body  depends  on 
the  quantity  of  matter  in  the  body,  and  not  upon  its  kind. 
A  pound  of  feathers  is  attracted  with  the  same  force  as  a 
pound  of  lead.    The  quantity  of  matter  in  a  body  is  called 


FIG.  14. 

The  two  balls 

attract  each 

other. 


MASS  AND  WEIGHT 


19 


the  mass  of  the  body.  The  weight  of  the  body  is  the  re- 
sult of  the  earth's  pull  upon  the  mass  of  the  body.  If,  in 
some  way,  the  pull  upon  a  given  body  is  increased,  the 
weight  will  be  in- 
creased; but  if  the 
pull  is  weakened,  the 
weight  will  be  de- 
creased. Now,  how 
can  we  change  the 
effect  of  gravity,  that 
is,  the  attraction  of 
the  earth  for  a  cer- 
tain mass?  We  can 
do  it  by  changing  the 
distance  between  the 
earth  and  the  body. 
In  other  words,  the 
attraction  between 
two  bodies  depends 
not  only  on  their 
masses,  but  also  on  the  distance  they  are  apart.  The 
distance  between  two  bodies  is  taken  to  be  the  distance 
between  their  centers. 

Suppose  we  have  two  balls  weighing,  say,  10  grams  each,  and  1  inch 
apart.  If  we  place  them  2  inches  apart,  the  force  of  the  attraction  be- 
tween them  will  be  only  %  as  great  as  at  1  inch.  If  the  distance  be- 
tween them  is  made  ^  an  inch,  the  attraction  will  be  4  times  what  it 
was  originally.  Now,  we  have  learned  that  the  earth  is  not  a  perfect 
sphere,  but  is  flattened  at  the  poles.  An  object  at  the  poles  is  about  13 
miles  nearer  the  earth's  center  than  if  it  were  at  the  equator.  As  a 
result  of  this  difference  a  body  weighing  589  pounds  at  the  equator 
would  weigh  590  pounds  at  the  poles. 


Copyright  International  Stereograph  Co.,  Decatur,  111. 


FIG.  15. 
Leaning  Tower  of  Pisa. 


20  FORCE  AND  ENERGY 

If  we  remove  a  body  from  the  earth  at  any  given  place,  that  is,  if  we 
take  it ' 'up  in  the  air,"  or  on  a  mountain  top,  it  will  also  lose  in  weight. 
The  mass  of  the  body  will,  of  course,  remain  the  same  everywhere. 

21.  Falling  Bodies. —  We  know  that  if  we  drop  a  stone 
it  falls  "straight  down."  We  have  also  seen  bricklayers 
using  a  string  with  a  weight  attached— 
a  plumbline  —  to  be  sure  that  they  were 
making  a  wall  vertical.  The  position  taken 
by  the  plumbline,  like  the  path  of  the 
falling  ball,  shows  that  gravity  pulls  ver- 
tically downward. 

But   objects  that    are   very  light,   like 
feathers,   seem  to  fall  more  slowly  than 
heavy    objects.     Why    is    this?     Galileo, 
dropping  balls  of  different  sizes  and  differ- 
ent materials  from  the  "leaning  tower"  of 
Pisa  (Fig.   15),  insisted  that  all   objects, 
FIG.  16.         heavy  and  light,  if  let  fall  from  the  same 
Bodieva^uumgina    height,   should  reach   the   ground  at   the 
same  time.     A  feather  and  a  bullet  would 
fall  at  the  same  rate  were  it  not  for  the  air,  which  resists 
being  pushed  out  of  the  way.     In  a  tube  free  from  air,  that 
is,  in  a  vacuum  (Fig.  16)  they  do  fall  at  the  same  rate. 

On  a  very  windy  day  even  a  heavy  body  may  not  fall  straight  down. 
Thus  an  apple  blown  off  the  tree  by  a  sudden  gust  will  go  in  the  direc- 
tion of  the  wind  (horizontally)  and  also  downward.  It  cannot  go  in 
either  of  these  directions  alone,  so  it  goes  down  in  a  curved  path.  But 
it  will  reach  the  ground  by  the  longer,  curved  path  in  the  same  time 
as  if  it  fell  vertically  to  the  ground.  This  fact  may  be  illustrated  by 
two  marbles  (Fig.  17)  one  of  which  is  given  a  horizontal  blow,  while 
the  other  is  permitted  to  fall  vertically. 


FORCE  21 


22.  Exercises. 


1.  Name  five  phenomena,  besides  those  of  §  18,  that  are  "changes 
in  the  position  of  bodies." 

2.  Suppose  that  the  moon  and  the  earth  were  of  exactly  the  same 
mass,  and  that  a  ball  weighing  a  ton  were  placed  half-way  between 
them.     What   would   its   weight   be? 

Why? 

3.  If  you  dropped  wooden,  iron,  and 
lead  balls  from  an  upper  window,  which 
would  reach  the  ground  first? 

4.  Suppose  the  wind  were  blowing 
hard  down  the  street,  and  you  dropped 
a  tennis  ball  from  an  upper  window. 
Where  would   it    strike   the   ground? 
Why? 

5.  Draw  a  diagram  to  show  the  kind     The  Marbleg  ^  &t  ^ 
of  a  path  a  ball  takes  if  you  throw  it                    Same  instant. 
horizontally.    If  you  throw  it  upward 

at  an  angle  of  45  degrees  (half  a  right  angle).    In  which  case  would 
the  ball  have  the  greater  range? 

6.  Who  was  Sir  Isaac  Newton?    When  did  he  live,  and  where? 
What  did  he  add  to  our  knowledge? 

Answer  the  same  questions  regarding  Galileo. 

23.  Force. —  Let  us  imagine  we  are  at  a  baseball  game. 
The  pitcher  throws  a  "fair"  ball,  the  batter  strikes  at  it 
but  makes  a  "foul"  hit,  and  the  catcher  catches  the  ball. 
Three  persons  were  concerned  in  the  flight  of  that  ball: 
the  pitcher,  who  set  it  in  motion ;  the  batter,  who  changed 
the  direction  of  its  motion;  and  the  catcher,  who  stopped 
its  motion.  We  say  that  all  three  exerted  force  upon  the 
ball. 

Besides  the  players,  two  other  bodies  exerted  force  upon 
the  pitched  ball:  (1)  the  air,  which  resisted  being  pushed 


22 


FORCE  AND  ENERGY 


out  of  the  way  and  hence  made  the  ball  move  more  and 
more  slowly;  (2)  the  earth,  which  by  its  downward  pull 
made  the  ball  move  in  a  path  curving  downward  instead 
of  in  a  horizontal  one. 

This  illustration  shows  us  the  ways  in  which  one  body 
may  exert  force  upon  another:  (1)  it  may  set  the  other 
body  in  motion;  (2)  it  may  change  the  direction  of  the 
motion;  (3)  it  may  stop  the  motion.  In  addition,  (4)  one 
body  may  change  the  velocity,  or  rate  of  motion,  of  another 
and  so  exert  force  upon  it. 

Air  exerts  force,  not  simply  by  resisting  other  bodies 
as  they  pass  through  it,  but  also  as  wind  —  air  in  motion. 
We  use  the  force  of  the  wind  to  sail  a  kite,  to  run  a  wind- 
mill, or  to  drive  a  ship  through  the  sea. 

24.  Force  of  Expanding  Gases. —  What  exerts  the  force 
that  sets  a  bullet  in  motion?  The  cartridge  used  in 
modern  firearms  is  partly  filled  with  powder  (Fig.  18), 
and  the  open  end  of  the  cartridge  is  closed  by  the  bullet. 

Besides  powder,  the  cartridge 
contains  a  small  amount  of  a 
white  solid  called  mercury  ful- 
minate, which,  when  given  a 
blow  (percussion),  sets  the  pow- 
der on  fire.  The  pulling  of  the 
trigger  releases  the  hammer  of 

the  gun;  the  blow  of  the  hammer  causes  the  mercury 
fulminate  to  ignite  the  powder,  so  that  it  "explodes." 
By  the  explosion  of  the  powder  a  gas  is  formed  that  will 
take  up,  when  released,  perhaps  300  times  as  much  space 
as  the  original  powder.  In  the  cartridge  the  gas  is  under 


FIG.  18. 

Kinds    of    Powder:     (1)    Ordinary 
Form;  (2)  Giant  Powder. 


FORCE  OF  EXPANDING  GASES 


23 


great  pressure,  because  it  is  crowded  into  so  small  a 
space.  As  it  rushes  out  of  the  cartridge  it  expands,  and 
drives  the  bullet  rapidly  before  it. 

The  steam  engine,  like  the  gun  and  cannon,  is  a  device  for  producing 
motion  by  means  of  the  expansion  of  a  compressed  gas.  Steam  is  pro- 
duced, under  high  pressure,  in  a  boiler  (Fig.  19),  and  is  allowed  to  ex- 
pand in  a  cylinder,  first  on  one  side  and  then  on  the  other,  of  a 


FIG.  19. 
Principle  of  the  Steam  Engine. 

piston.  The  piston  is  thus  moved  rapidly  to  and  fro.  This  forward  and 
backward  motion  is  then  changed  to  motion  in  a  circle  by  means  of  a 
shaft.  The  eccentric  turns  with  the  shaft  and  moves  the  slide  valve. 
The  cause  of  motion  in  a  gasoline  engine  is  also  the  force  exerted  by 
expanding  gases.  A  mixture  of  gasoline  vapor  and  air,  which  is  ex- 
ploded by  an  electric  spark  or  a  hot  wire,  is  used  in  place  of  steam. 
The  explosion  produces  a  large  volume  of  hot  gases,  and  the  expansion 
of  the  gases  sets  a  piston  in  motion. 

The  force  exerted  in  the  examples  given  may  be  put  in 
one  of  the  following  classes : 


24  FORCE  AND  ENERGY 

(1)  Muscular  force,  such  as  that  exerted  by  draught 
animals  and  man. 

(2)  Gravity. 

(3)  The  force  of  the  wind. 

(4)  Resistance,  such  as  that  of  air,  water,  the  ground, 
or  the  parts  of  machinery.     We  commonly  call  this 
friction  (cf.  §  206). 

(5)  The  force  of  expanding  gases. 

Of  course  one  body  may  exert  force  upon  another  and 
yet  not  move  it,  as  when  you  try  to  lift  a  weight  too 
heavy  for  you. 

25.  Work  and  Energy. —  When  we  raise  a  hammer 
into  the  air,  we  do  work  upon  it,  for  we  lift  it  against  grav- 
ity. We  also  do  work  when  we  throw  a  ball,  or  wind  up 
a  watch.  In  the  last  case  we  produce  motion  against  the 
elastic  force  of  the  spring.  Because  we  can  do  work,  we 
say  we  have  energy.  Energy  is  the  capacity  for  doing 
work.  A  body  that  can  do  work  upon  another  body 
possesses  energy. 

The  lifted  hammer  has  energy  because  we  have  done 
work  upon  it,  and  it,  in  its  turn,  can  do  work  upon  some 
other  body.  If  we  let  it  fall,  it  can  break  a  nutshell  or 
drive  a  nail  into  wood.  While  poised  in  the  air,  the 
hammer  has  energy  because  of  its  position;  while  it  is  de- 
scending it  has  energy  of  motion.  In  the  same  way,  the 
water  of  a  waterfall  has  energy  of  position  at  the  top  of 
the  fall,  but  energy  of  motion  as  it  descends. 

A  bullet  in  a  gun  at  the  instant  of  discharge  can  be  said  to  have 
energy  of  position  because  of  the  compressed  gas  behind  it.  In  its 
flight  it  has  energy  of  motion.  When  it  strikes  a  rock  or  a  tree  or  other 


INERTIA  OF  MATTER 


25 


obstruction,  it  does  work:  it  breaks  the  rock,  or  splits  the  tree,  or  flat- 
tens itself. 

When  a  body  does  work  by  lifting  another  body  against  gravity,  the 
amount  of  work  done  is  obtained  by  multiplying  the  weight  lifted 
by  the  vertical  distance  it  is  lifted: 

Work  =  weight  X  distance. 

Thus,  a  workman  carrying  50  Ibs.  up  a  ladder  20  ft.  high  does  just 
as  much  work  as  one  raising  40  Ibs.  25  ft.,  or  10  Ibs.  100  ft. 

26.  Power. —  In  calculating  the  amount  of  work  done 
by  a  force  we  have  not  taken  account  of  the  time  required. 
Yet  if  we  were  choosing  a 
horse  or  an  engine  to  raise 
a  weight  (Fig.  20),  we  would 
take  the  horse  or  engine  that 
could  do  the  work  most  rap- 
idly.   The  rate  of  doing  work 
is  power. 

The  common  unit  of  power 
is  the  horse-power  (written 
H.P.) .  James  Watt,  who  de- 
vised the  unit,  thought  that 

an  average  horse  could  raise  33,000  Ibs.  1  ft.  in  1  minute, 
or  550  Ibs.  1  ft.  in  1  second.  As  a  matter  of  fact,  the 
average  American  horse  can  exert  only  about  three- 
fourths  of  a  horse-power;  that  is,  it  can  raise  about  25,000 
Ibs.  1  ft.  in  1  minute. 


FIG.  20. 
Horse  Raising  Weight  of  a  Pile-Driver. 


27.  Inertia  of  Matter. —  In  Chapter  I  we  learned  that 
matter  occupies  space  and  has  weight.  What  we  have 
now  learned  about  force  shows  us  that  matter  has  another 


26  FORCE  AND  ENERGY 

striking  property  —  helplessness.  This  property  is  com- 
monly called  inertia.  We  define  inertia  when  we  say  that 
matter  cannot  move  itself,  cannot  stop  itself  if  moving, 
and  cannot  change  the  direction  or  rate  of  its  motion. 

There  are  many  illustrations  of  inertia  :  — 

When  you  played  "tag,"  and  your  playmate  came  rushing  toward 
you  at  full  speed,  you  took  advantage  of  the  inertia  of  his  body  when 
you  l  '  dodged."  You  knew  he  could  not  stop  himself  at  once. 

When  you  run  around  a  corner,  you  go  in  a  wide  curve,  because  the 
inertia  of  your  body  will  not  let  you  turn  the  corner  sharply. 

When  you  shake  a  rug,  you  are  able  to  jerk  the  rug  away  from  the 
dirt  because  of  the  inertia  of  the  dirt. 

If  you  hit  a  suspended  newspaper,  you  burst  a  hole  in  it,  because 
only  the  part  struck  moves  forward  while  the  rest  of  the  newspaper 
remains  behind. 

The  air  also  has  inertia.  If  we  try  to  push  it  away  suddenly,  as  by 
thrusting  forward  a  paper  fastened  in  a  large  hoop,  the  air  remains 
where  it  was  and  tears  the  paper,  just  as  a  tree  or  a  rock  would.  We 

work  against  the  inertia  of  air  in  mo- 


;/'  N\  against  a  strong  wind,  or  to  "haul  in" 

/  \        a  sail  in  a  gale. 

» 
\ 

\        28.  "  Flying  from  the  Cen- 
/     ter."  —  If  a  stone  attached  to 
/      a  string  is  whirled  about  the 
hand,  it  moves  in  a  circle  (Fig. 
^^x  21).    The  circular  path  is  the 

FIG.  21.  result  of   two   forces:   (1)   the 

The  Circular  Path  is  the  Result  of          inertia      rvf      tVm     rnr^nncr     c+rmo 

inertia  and  the  string.  uiertia   oi    me   moving   stone, 

which,  acting  alone,  would  cause 

the  stone  to  move  off  in  a  straight  line;  and  (2)  the  re- 
sistance of  the  string,  which  compels  the  stone  to  remain 


EXERCISES  27 

always  at  the  same  distance  from  the  hand.  Because 
of  the  inertia  of  the  moving  stone  we  feel  a  decided 
pull  upon  the  string.  The  pull  becomes  the  stronger  the 
more  rapidly  the  stone  is  whirled.  Finally  the  pull  may 
break  the  string.  If  it  does,  the  stone  will  fly  off  in  a 
straight  line. 

This  tendency  of  the  matter  of  a  revolving  body  to 
fly  off  in  a  straight  line  is  called  centrifugal  force.  ' '  Cen- 
trifugal" comes  from  words  meaning  "to  fly  from  the 
center."  Centrifugal  force  is  really  no  new  kind  of  force, 
but  merely  a  result  of  the  inertia  of  matter. 

The  flying  off  of  mud  from  a  revolving  carriage  wheel,  and  of  water 
from  a  turning  grindstone,  and  our  difficulty  in  turning  a  sharp  corner 
when  we  are  running,  are  familiar  illustrations  of  centrifugal  force. 
The  planets  continue  in  their  paths  around  the  sun  because  of  inertia 
together  with  the  attraction  between  them  and  the  sun.  The  dairy 
separator  is  an  apparatus  for  separating  cream  from  milk  by  rapid 
whirling.  In  this  apparatus  centrifugal  force  causes  the  milk,  which 
is  the  heavier,  to  move  out  farther  than  the  cream,  and  so  divides  them. 

29.  Exercises. 

1.  Why  is  it  so  hard  to  walk  upon  a  polished  floor?    Why  is  it  easier 
to  skate  on  ice  than  to  walk  upon  it? 

2.  Why  does  not  gravitation  draw  the  sun  and  earth  together? 

3.  On  which  will  a  marble  roll  farther,  a  carpet  or  a  smooth  floor? 
Why?     Suppose  we  could  roll  the  marble  on  a  perfectly  smooth, 
horizontal  plane,  what  force  would  there  be  to  stop  the  marble? 

4.  When  you  strike  the  lowest  of  a  pile  of  blocks  a  sharp  blow,  it 
flies  out,  leaving  the  rest  of  the  blocks  piled  up.    Why? 

5.  What  happens  to   a  child  sitting   on  a  sled  if   the  sled  is 
suddenly  started?    If  the  moving  sled  is  suddenly  stopped?    In  what 
direction  is  the  child  thrown  off  if  the  sled  turns  a  sharp  corner? 
Explain. 


28 


FORCE  AND  ENERGY 


6.  What  work  was  done  upon  the  water  of  a  waterfall  to  give  it 
energy? 

7.  What  device  is  used  to  prevent  a  railway  train  from  leaving  the 
track  when  rounding  a  curve?    Is  any  similar  device  used  in  a  gym- 
nasium?   On  an  automobile  or  motorcycle  race  course? 

30.  Cohesion  and  Adhesion. —  If  we  hold  a  sheet  of 
glass  face  down  against  the  surface  of  some  water,  and 
then  pull  the  glass  away  from  the  water,  we  must  use 
more  force  than  is  needed  to  lift  the  glass  against  gravity 
alone.  Another  force  is  being  exerted  on  the  glass.  The 
under  side  of  the  glass  will  be  wet.  This  shows  that  in 
pulling  the  glass  away  we  did'  not  separate  glass  from 
water,  but  water  from  water.  We  therefore  did  work 

(cf.  §  25)  against  the  force  that 
holds  the  water  together.  The 
force  that  is  exerted  between 
the  particles  of  matter  is  called 
cohesion. 

We  can  find  the  amount  of  cohesion, 
in  the  case  of  water,  by  attaching  a 
piece  of  glass  by  means  of  strings  to 
one  arm  of  a  balance  (Fig.  22),  allowing 
the  glass  to  touch  the  water,  and  then 
adding  weights  to  the  other  side  of  the 
balance  until  we  tear  the  glass  away. 

Of  course  we  must  subtract  the  weight  of  the  glass  from  the  total 

weight  to  get  the  ''breaking  weight"  of  the  water. 


FIG.  22. 

Measuring  the  Force  Needed  to 
Tear  Water  from  Water. 


When  cohesion  is  exerted  between  different  substances, 
we  call  it  adhesion.  Thus  cohesion  holds  water  together, 
and  cohesion  holds  glass  together,  but  adhesion  holds 


THE  SURFACE  OF  A  LIQUID 


29 


water  to  glass.  Since  we  pull  water  away  from  water, 
we  see  that  the  cohesion  of  water  is  not  as  strong  as  the 
adhesion  of  water  to  glass. 

Cohesion  in  solids  causes  them  to  be  rigid;  that  is,  to 
resist  being  strained  or  broken. 

31.  The  Surface  of  a  Liquid. —  We  know  that  large 
liquid  surfaces  are  flat  (horizontal) ;  this  is  because  grav- 
ity pulls  down  equally  on  all  parts  of  the  surface.  But 
when  the  body  of  liquid  is  very  small  (a  drop),  the  effect 
of  gravity  is  also  small,  and  cohesion  is  able  to  pull  the 
liquid  into  the  shape  of  a  sphere.  This  is  exactly  the 
shape  that  would  be  produced  if  the  liquid  were  enclosed 
in  a  tightly  stretched,  elastic  covering,  say,  of  rubber. 

The  shape  of  a  drop  of  liquid  depends  on  cohesion 
alone,  but  a  quantity  of  liquid  in  a  vessel  is  acted  upon 
by  three  kinds  of  force,  and  the  shape  of  its  surface  will 
depend  on  all  three.  These  are:  (1)  gravity,  (2)  cohesion 
of  the  liquid,  (3)  adhe- 
sion between  the  liquid 
and  the  material  of  the 
vessel. 


FIG.  23. 

Surfaces  of  Water  (A)  and  Mercury  (B). 


Let  us  take  the  case  of  mer- 
cury in  a  glass  vessel  (Fig.  23, 
B).  Mercury  does  not  wet 
glass.  This  means  that  the 
cohesion  of  mercury  is  greater 

than  the  adhesion  between  mercury  and  glass.     Hence  the  surface 
of  the  mercury  curves  outwards,  or  is  convex,  like  the  surface  of  a  drop. 

The  case  of  water  in  a  glass  vessel  is  different  (Fig.  23,  A):  water 
wets  glass.  This  means  that  the  adhesion  between  water  and  glass  is 
greater  than  the  cohesion  of  water.  In  such  cases  the  liquid  is  drawn 


30 


FORCE  AND  ENGERY 


FIG.  24. 

A  Needle  Floating  on 
Water. 


up  at  the  edges,  and  the  surface  curves  inwards,  or  is  concave  ("hol- 
lowed out"). 

In  a  greased  vessel  water  has  a  convex  upper  surface,  like  that  of 
mercury  in  a  glass  vessel.  The  cohesion  of  water  is  evidently  stronger 
than  the  adhesion  between  water  and  grease. 

The  curved  surface  of  a  liquid  is  called  a  meniscus.    In 
reading  the  level  of  water  in  a  graduated  cylinder  (Fig.  5) 
we  read  at  the  bottom  of  the  meniscus. 
That  the  surface  of  a  liquid  acts  as 
though  it  were  an  elastic  covering,  and 
that  it  can  be  stretched,  is  shown  by  an 
experiment  in  which  a  needle  is  floated 
upon  water  (Fig.  24).    The  needle  must 
be  put  down  carefully,  or  it  will  break 
the  elastic  surface  of  the  water.    The  experiment  suc- 
ceeds  better   if    the   needle    is 
slightly  greased,  so  that  the  water 
is  certain  not  to  wet  it. 

32.  Capillary  Action. —  If  you 
leave  one  end  of  a  towel  in  a 
bowl  of  water,  the  water  rises, 
against  gravity,  into  the  towel. 
If  you  let  a  wet  string,  or>  bet- 
ter, a  wet  strip  of  cloth,  hang 
over  the  side  of  a  dish  of  water 
(Fig.  25),  the  water  will  rise 

through  the  string  or  cloth,  and  so  flow  out  of  the  dish. 
If  you  touch  a  drop  of  ink  with  a  blotter,  the  whole  drop 
will  flow  into  the  blotter.  What  causes  these  phenomena? 
We  say  that  the  force  exerted  in  these  cases  is  "  capillary  " 


FIG.  25. 

Water  Flowing  by  Capillary  Action 
Over  the  Side  of  a  Dish. 


DENSITY  AND  SPECIFIC  GRAVITY 


31 


B 


FIG.  26. 

A,  Capillary  Rise  of  Water;    B,  Capillary 
Depression  of  Mercury. 


action.  "Capillary"  means  "hairlike."  The  phenome- 
non is  so  called  because  it  is  commonly  studied  in  tubes 
of  small  diameter  (Fig.  26). 

Capillary  action  in  water  is  due  to  adhesion  between  the 
water  and  the  capillary  tube,  and  to  the  cohesion  of  the 
water,  which  produces  an 
elastic  surface.  If  the  tube 
is  a  large  one,  the  water  is 
raised,  but  only  at  its  edges, 
as  in  the  case  of  water  in  a 
dish.  The  elastic  surface 
cannot  exert  force  enough 
to  lift  all  the  water  in  the 
tube.  But  if  the  tube  is  of 
small  diameter  —  a  "  capillary  "  tube  —  the  weight  of  the 
water  in  the  tube  is  small,  and  the  elastic  liquid  surface 
lifts  the  whole  column  of  water  up  the  tube. 

Water  rises  in  a  capillary  tube  until  the  weight  of  the  water  is  just 
equal  to  the  force  exerted  by  the  elastic  surface.  The  upper  surface  of 
the  water  column  in  a  capillary  tube  is  still  concave. 

If  a  glass  capillary  tube  is  placed  in  mercury  (Fig.  26,  B),  the  effect 
is  the  opposite  of  that  in  water,  and  we  have  a  capillary  depression 
instead  of  elevation. 

Water  rises  up  between  two  glass  plates  held  close  together  just  as 
it  does  in  capillary  tubes.  In  the  case  of  the  blotter,  cloth,  string,  etc., 
the  fibers  of  the  material  are  so  near  one  another  that  the  spaces  be- 
tween them  act  like  a  multitude  of  fine  tubes. 

33.  Density  and  Specific  Gravity. —  If  you  were 
"hefting"  a  piece  of  wood  and  a  piece  of  lead,  you  would 
say  that  wood  is  a  light  substance  and  lead  a  heavy  one. 
In  saying  this  you  would  not  mean  that  a  large  board  of 


32  FORCE  AND  ENERGY 

wood  is  lighter  than  a  small  lump  of  lead,  but  you  would 
mean  that,  taken  volume  for  volume,  wood  is  lighter  than 
lead.  This  is  the  same  as  saying  that  the  density  of  wood 
is  less  than  the  density  of  lead  (Fig.  27). 

We  have  already  learned  that  the  mass  of  a  body  is 
the  quantity  of  matter  in  it  (c/.  §  20).    We  may  now  de- 


Gold.          Lead.  Copper.  Aluminum.  Coal.  Wood. 

FIG.  27. 
Cubes  of  Different  Volumes,  but  of  Equal  Weight 

fine  the  density  of  a  body  as  the  quantity  of  matter 
packed  in  a  given  volume  of  the  body.  To  get  the  mass  of 
a  body  we  weigh  it.  To  get  the  density  of  a  body  we 
divide  its  weight,  in  grams,  by  its  volume,  in  cubic 
centimeters. 

mass  (in  g.) 


Density  = 


volume  (in  c.c.) 


Suppose  that  a  piece  of  marble  weighs  5  g.  and  has  a  volume  of  2 
c.c. ;  it  is  plain  that  1  c.c.  of  the  marble  would  weigh  2.5  g.  We  say  that 
the  marble  has  a  density  of  2.5  g.  for  each  cubic  centimeter.  The  den- 
sity of  water  is  1  g.  for  each  cubic  centimeter  (c/.  §  14).  In  the  Eng- 
lish system  the  density  of  water  is  about  62.5  Ibs.  for  each  cubic  foot. 

We  often  find  the  expression  specific  gravity  used  in  place  of  density. 
We  get  the  specific  gravity  of  a  body  by  dividing  the  weight  of  the 
body  by  the  weight  of  an  equal  volume  of  water. 

Wt.  of  body 
Specific  gravity  = 


Wt.  of  equal  vol.  of  water 


BUOYANT  FORCE  OF  LIQUIDS 


33 


When  the  density  of  a  body  is  given  as  so  many  grams  for  1  c.c., 
the  number  representing  the  density  is  the  same  as  the  number  for  the 
specific  gravity. 

34.  Buoyant  Force  of  Liquids. —  If  we  attach  a  string 
to  a  block  of  wood,  and  lift  the  wood  by  the  string,  we 
need  to  put  forth  a  muscular  effort  equal  to  the  weight  of 
the  wood.  But  if  we  let  the  block  rest  on  water,  we  do 
not  put  forth  any  effort;  the  water  supports  the  block. 
We  say  that  the  block  floats  on  the  water. 

If  we  hold  a  piece  of  stone  by  a  string,  first  in  air,  and 
then  in  water,  we  find  that  the  stone  is  lighter  (weighs 
less)  in  water  than  in  the  air.  Here  the  water  does  not 
support  all  of  the  weight,  but  it  does  support  part  of  it. 
It  is  well  known  that  a  stone  can  be  lifted  much  more 
easily  when  it  is  under  water 
than  when  it  is  out  of  the  water. 

Suppose  that  some  lead  is  cut  or  cast 
in  the  form  of  a  cube  having  a  volume  of 
exactly  1  c.c.,  and  is  attached  to  one  arm 
of  a  balance,  as  in  Fig.  28.  If  we  weigh 
it  in  air  and  then  in  water  we  shall  find 
that  it  weighs  1  gram  less  in  water  than 
in  the  air.  One  cubic  centimeter  of  iron, 
glass,  or  marble,  or  of  any  solid  which  is 
more  dense  than  water,  would  lose  the 
same  amount  —  1  gram  —  when  weighed 

in  water.  Since  the  1  c.c.  of  water  displaced  by  each  of  the  cubes 
weighs  just  what  the  cube  seems  to  lose,  we  conclude  that  a  body  put 
under  water  is  pushed,  or  buoyed,  up  by  just  the  amount  of  the 
water  it  displaces.  A  mass  of  iron,  stone,  glass,  etc.,  having  a  volume 
of  a  cubic  foot  would  weigh  62.5  pounds  less  in  water  than  in  the  air, 
since  this  is  the  weight  of  a  cubic  foot  of  water  (cf.  §  33). 


FIG.  28. 

A  Solid  Immersed  in  a  Liquid  is 
Buoyed  up  by  the  Liquid. 


34  FORCE  AND  ENERGY 

Not  only  water,  but  all  liquids  and  gases,  have  this 
buoyant  power.  The  more  dense  the  liquid  or  gas,  the 
greater  is  its  power  of  buoyancy.  Hence  we  may  state 
the  facts  regarding  buoyant  force  as  a  general  rule : — 

A  body  immersed  in  a  liquid  or  gas  is  buoyed  up  with  a 
force  just  equal  to  the  weight  of  the  liquid  or  gas  it  displaces. 

A  floating  body  sinks  into  the  liquid  supporting  it  until  it  has  pushed 
aside  its  own  weight  of  liquid.  Thus  a  piece  of  cork  34  as  dense  as 
water  sinks  until  %  of  its  volume  is  below  water.  A  piece  of  ice  0.92 
as  heavy  as  water  has  0.92  of  its  volume  below  water. 

A  needle  (cf.  §  31)  has  really  a  much  greater  density  than  water, 
but  it  can  be  supported  on  water  because  its  weight  is  very  small.  As 
a  result  the  elastic  surface  of  the  water  does  not  break.  If  the  needle 
becomes  wet,  the  water  surface  breaks,  and  the  needle  sinks. 

35.  Center  of  Mass. —  Why  does  a  slender  stick 
which  has  been  set  upright  fall  over  so  easily?  Why 
cannot  we  stand  an  egg  "on  end"?  The  answer  is 
found  in  a  study  of  the  center  of  mass  of  a  body. 
We  all  know  what  is  meant  by  the  center  of  a  sphere: 
it  is  the  point  around  which  the  volume  of  the 
sphere  is  arranged  in  a  regular  way.  Let  us  call  this  cen- 
ter the  center  of  volume  of  the  sphere.  Now,  in  a  wooden 
ball  or  a  lead  ball  the  matter ,  as  well  as  the  volume,  is  all 
grouped  around  the  center;  so  we  can  call  the  center  of 
volume  the  center  of  mass,  or  center  of  gravity,  of  the  ball. 

If  we  were  to  mix  small  fragments  of  lead  and  sawdust 
uniformly  together,  and  pack  thejn  into  a  ball,  the  center 
of  mass  of  the  ball  would  still  be  the  same  as  its  center  of 
volume.  But  if  we  were  to  make  half  of  the  ball  of  wood 
and  the  other  half  of  lead,  and  were  to  fasten  the  two 


CENTER  OF  MASS 


35 


halves  together,  the  center  of  mass  of  the  ball  would  not 

be  the  same  as  its  center  of  volume.     Lead  is  so  much 

denser  than  wood  that  the  center  of  mass  would  be 

somewhere  in  the 

lead  half  of  the       / 

ball  (Fig.  29).   In     /Lead  wood\ 

an  egg  the  center     \ 

of  mass  is  nearer      \ 

the   larger  than 

the  smaller  end. 

A  body  IS  in  its  The  Ball  Takeg  Pogition  (2)  The  Heavy  Knife  Handles  (3) 
most  ' '  Stable  "  pOSi-  Bring  the  Center  of  Mass  Below  the  Tip  of  the  Pencil. 

tion,  that  is,  is  best 

able  to  stand,  when  the  center  of  its  mass  is  lowest,  or  nearest  the 
earth's  center.  A  ball  of  wood  is  at  rest  in  any  position,  because  its 
center  of  mass  is  as  low  in  one  position  as  in  another,  but  a  ball 
half  wood  and  half  lead  will  be  in  a  stable  position '  only  when  the 
lead  half  is  the  lower.  An  egg  lies  on  its  side  but  not  on  end  because 
when  it  is  on  its  side  its  center  of  mass  is  lower.  To  make  it  stand  on 
end  we  would  need  to  keep  its  center  of  mass  exactly  above  the  point  at 
which  it  rests  upon  the  table  or  other  support.  As  we  cannot  do  this, 
the  egg  rolls  over.  We  ourselves  stand  when  we  keep  the  center  of 
mass  of  our  bodies  above  the  space  bounded  by  our  feet,  but  we  fall 
when  we  lean  over  so  far  that  our  center  of  mass  is  no  longer  vertically 
above  this  space. 

When  an  irregular  body,  such  as  a  log  or  tree,  lies  on  the  ground,  it 
cannot  shift  itself  so  that  it  can  bring  its  center  of  mass  to  the  lowest 
position,  but  if  we  float  the  body  upon  water,  it  turns  over  until  it 
finds  this  position. 

36.  Summary. —  Gravitation  is  the  pull,  or  attraction,  existing  be- 
tween all  bodies  of  matter. 

Gravity  is  the  earth's  pull  upon  bodies  at  or  near  its  surface.  Grav- 
ity pulls  vertically  downward,  that  is,  toward  the  earth's  center. 


36  FORCE  AND  ENERGY 

The  mass  of  a  body  is  the  amount  of  matter  in  it. 

The  amount  of  attraction  between  bodies  depends  on  the  masses  of 
the  bodies  and  on  the  distance  they  are  apart. 

The  weight  of  a  body  represents  the  earth's  attraction,  at  any  given 
place,  for  the  mass  of  the  body. 

A  body  weighs  more  at  the  earth's  poles  than  at  the  equator,  and 
more  at  the  earth's  surface  than  "up  in  the  air."  The  mass  does  not 
change. 

In  a  vacuum  all  bodies  fall  with  the  same  speed. 

If  a  falling  body  is  acted  upon  by  a  horizontal  force,  its  path  is 
curved;  but  the  time  taken  is  the  same  as  if  gravity  acted  alone. 

Force  is  exerted  on  a  body  by  the  muscles  of  men  and  animals,  by 
the  earth  (gravity),  by  the  wind,  by  other  bodies  (as  resistance  or  fric- 
tion), by  expanding  gases,  etc. 

A  body  on  which  work  has  been  done  has  energy,  or  the  capacity  for 
doing  work  on  other  bodies. 

There  is  energy  of  position  and  energy  of  motion. 

Work  (against  gravity)  =  weight  X  vertical  distance. 

Power  is  the  rate  of  doing  work. 

Inertia  is  the  helplessness  of  matter  to  alter  its  condition  of  rest  or 
motion. 

"Centrifugal  force"  is  the  pull  of  matter,  when  revolving,  against 
whatever  holds  it  to  the  center. 

The  force  that  is  exerted  between  the  particles  of  matter  and  holds 
matter  together  is  called  cohesion,  or  adhesion. 

The  cohesion  of  liquids  causes  them  to  form  drops,  and  to  have  elas- 
tic surfaces. 

The  upper  surface  of  a  liquid  that  does  not  adhere  to  the  vessel  is 
like  a  flattened  drop;  that  is,  convex. 

If  the  liquid  wets  the  vessel,  the  surface  is  concave. 

The  cohesion  of  liquids  and  their  adhesion  to  solids  (wetting) 
causes  the  liquids  to  rise  in  narrow  spaces  or  tubes.  This  is  "capillary 
action." 

The  density  of  a  body  or  a  substance  is  the  quantity  of  matter  in  a 
.given  volume.  Pure  water  at  4°  C.  has  a  density  of  1. 

Buoyant  force  is  the  supporting,  or  lifting,  power  of  liquids  and  gases. 


EXERCISES  37 

A  floating  body  is  entirely  supported.  An  immersed  body  is  supr 
ported  with  a  force  equal  to  the  weight  of  the  liquid  (or  gas)  displaced 
by  the  body. 

The  center  of  mass  of  a  body  is  the  point  around  which  the  matter 
of  the  body  is  arranged.  A  body  is  in  a  stable  position  when  its  center 
of  mass  is  directly  over  some  part  of  the  base  on  which  the  body  rests. 
It  is  most  stable  when  its  center  of  mass  is  in  the  lowest  possible  posi- 
tion. 

37.  Exercises. 

1.  What  is  the  chief  force  to  be  overcome  when  we  drive  a  nail  into 
wood? 

2.  Why  does  a  drop  of  mercury  on  a  table  remain  almost  spherical, 
while  a  drop  of  water  does  not? 

3.  Why  is  it  so  hard  to  dry  the  hands  on  a  new,  unlaundered  towel? 
Why  is  writing  paper  " filled"  or  " sized"? 

4.  Name  the  following  substances  in  the  order  of  their  densities, 
beginning  with  the  lightest  (see  Appendix,  Table  III):    iron,  cork, 
kerosene,  lead,  paraffin,  aluminum,  marble,  zinc,  gold,  silver,  copper, 
water,  alcohol,  and  milk. 

5.  If  one  cubic  foot  of  water  weighs  62.5  Ibs.,  how  much  does  a  cubic 
foot  of  iron  weigh? 

6.  How  does  the  addition  of  a  life  preserver  to  a  person's  body  alter 
the  weight  of  matter  that  must  be  supported  by  the  water?   How  does 
it  alter  the  density?    Why? 

.7.  Why  does  a  steel  ship  float? 

8.  We  can  find  the  volume  of  a  body,  such  as  a  stone,  if  we  weigh 
the  body  first  in  air  and  then  in  water.    Explain  how. 

9.  An  iceberg  may  turn  over  after  the  part  under  water  has  melted 
for  a  time.    Why? 

10.  How  do  you  lean  your  body  when  you  carry  a  pail  of  water? 
When  you  run  forward?    When  you  climb  a  hill?    Why? 


CHAPTER  III 

AIR  AND  FIRE 

38.  The  Atmosphere. —  As  we  already  know,  the  earth 
has  a  diameter  of  about  7,900  miles.  By  means  of  wells, 
of  cracks  in  the  earth,  and  of  deep  mines  the  solid  surface 
has  been  studied  to  a  depth  of  about  6,000  feet.  This 

outer  layer  is  called  the  crust  to 
distinguish  it  from  the  unknown 
interior,  or  core.  Filling  the  great 
hollows  of  the  crust  is  a  layer  of 
water,  which,  if  it  were  spread 
evenly  over  the  crust,  would 
cover  all  the  land  to  a  depth  of 
about  two  miles.  Finally,  sur- 
rounding both  land  and  sea  is 
the  ocean  of  gas  —  the  atmos- 
phere (Fig.  30) .  The  atmosphere 
extends  outward  from  the  crust 
an  unknown  distance,  but  most  of  it  is  within  50  miles 
of  the  earth's  surface.  Half  of  it  is  within  four  miles. 
The  substance  that  makes  up  the  atmosphere  is  air. 

Because  air  is  a  gas,  and  therefore  difficult  to  handle, 
men  looked  upon  it  for  a  long  time  as  a  mysterious,  un- 
knowable part  of  the  earth.  Only  when  men  became  used 
to  the  idea  that  air  and  other  kinds  of  gaseous  matter  are 
not  really  different  from  solid  and  liquid  matter  was  it 

38 


FIG.  30. 

Ideal  Section  of  the  Earth.    Thick- 
ness of  the  outer  layers  greatly 
exaggerated. 


ATMOSPHERIC  PRESSURE  39 

possible  for  them  to  get  a  thorough  knowledge  of  many  of 
our  common  phenomena.  We  now  know  that  the  atmos- 
phere contains  gases  and  living  forms  of  great  activity, 
and  that  these  have  very  important  effects  upon  the  sub- 
stances and  the  living  things  of  the  earth's  surface.  Thus, 
the  respiration,  or  breathing,  of  animals  and  plants,  and 
the  decay  of  all  substances  of  animal  and  vegetable  origin, 
are  due  to  the  air.  So  are  the  rusting,  or  tarnishing,  of 
metals,  and  the  phenomenon  of  fire,  or  burning. 

39.  Weight  of  Air. —  The  atmosphere  is  drawn  toward 
the  earth's  center  as  all  other  bodies  are;  hence  air  has 
weight  (cf.  §  4).    One  liter  of  air  ordinarily  weighs  about 
1.2  grams.    It  takes  a  little  over  4  liters  (about  a  gallon) 
to  weigh  as  much  as  a  nickel  five-cent  piece;  that  is,  5 
grams. 

We  can  get  an  idea  of  the  weight  of  air  in  another  way: — 
A  room  20  x  20  x  10  feet  holds  4,000  cubic  feet  of  air.    One  cubic 
foot  of  air  weighs  about  1M  ounces;  hence  the  air  of  the  room  weighs 
4,000X1  M,  or  5,000  ounces.     Dividing  this  by  16  we  get  312.5,  the 
weight  in  pounds. 

40.  Atmospheric  Pressure ;  the  Barometer. —  Because 
air  has  weight,  it  exerts  pressure  on  all  bodies  in  it,  and 
on  the  earth,  which  supports  it.     That  the  atmosphere 
has  pressure  was  first  proved  by  Torricelli  (pronounced 
Tor-ri-tchell-y),  a  pupil  of  Galileo,  in  1643.    Finding  that 
no  pump  could  lift  water  higher  than  32  feet  above  the 
water  of  a  well,  he  reasoned  that  this  was  probably  the 
greatest  height  to  which  the  atmospheric  pressure  could 
push  a  water  column.     If  this  were  so,  then  a  mercury 


40 


AIR  AND  FIRE 


FIG.  31. 

Filling    a    Barometer 

Tube  and  Inverting 

It  in  Mercury. 


column  ought  to  be  raised  only  about  1/13  as  high,  since 
mercury  is  about  13  times  as  dense  as  water. 

The  apparatus  Torricelli  used  to  test  his  conclusion  (Fig. 
31)  was  a  glass  tube  about  a  meter  long  and  closed  at  one 
end.  He  filled  the  tube  entirely  with 
mercury,  closed  the  open  end  with  his 
finger,  and  inverted  the  tube  in  a  vessel 
of  mercury.  When  he  removed  his  fin- 
ger, some  of  the  mercury  in  the  tube  ran 
out,  but  it  stopped  when  the  level  was 
about  29  inches  (that  is,  */„  of  32  ft.) 
above  the  mercury  in  the  vessel.  It  did 
not  fall  lower  because  the  pressure  of  the 
atmosphere  held  it  up. 

We  can  also  make  a  barometer  out  of 
a  tube  open  at  both  ends,  if  we  put  one 
of  the  ends  under  mercury,  and  remove  the  air  of  the  tube 
by  means  of  an  air  pump.  The  mercury  will  rise  about  30 
inches,  but  not  higher. 

The  simple  barometer  is  still  made  as  Torricelli  made  it.  The  ver- 
tical distance  between  the  top  of  the  mercury  in  the  tube  and  the 
mercury  in  the  vessel  is  called  the  height  of  the  barometer.  The 
barometer  height  changes  as  the  atmospheric  pressure  changes.  Its 
average  at  sea  level  is  about  760  mm.  (30  inches) ;  hence  this  is  called 
standard  pressure,  or  a  pressure  of  one  atmosphere.  The  space  above  ' 
the  mercury  is  a  vacuum. 

We  can  readily  calculate  the  atmospheric  pressure  from  the  barom- 
eter height.  If  the  column  of  mercury  in  the  barometer  is  1  square 
inch  in  cross  section,  and  30  inches  high,  it  has  a  volume  of  30  cubic, 
inches.  Now,  30  cubic  inches  of  mercury  weigh  about  15  Ibs.  Hence 
the  atmosphere  presses  down  upon  every  square  inch  of  matter  at  the 
earth's  surface  with  a  force  of  15  Ibs. 


PUMPS 


41 


Height 

n  Miles 

35 


Baro- 
meter 

n&es 


41.  Changes  in  Atmospheric  Pressure. —  If  you  were 
at  the  bottom  of  a  haystack,  trying  to  work  your  way  up 
through  it,  you  would  have  the  hardest  time  at  the  bot- 
tom, and  the  task  would  become  easier  as  you  approached 
the  top.    The  reason  is  that  the  hay  is  most  compact,  or 
dense,  in  the  lowest  layers,  since  these  layers  have  to  bear 
the  weight  of  all  the  hay  above  them.    So  it  is  with  the 
atmosphere :  its  lower  layers  are  crowded  together  by  the 
weight  of  the  air  they  support. 

That  this  is  so  is  proved  by  the  bwhavior  of  a  barometer  as  we  carry 
it  up  a  mountain  or  up  in  a  balloon.  The  mercury  column  falls  more 
and  more,  showing  that  the  density  and  the  pressure  of  the  air  grow 
smaller  as  we  ascend  (Fig.  32).  At  a  height  of  less  than  4  miles  the 
barometer  height  is  about 
380  millimeters,  or  15  inches; 
hence  half  of  the  atmosphere 
is  within  four  miles  of  the 
earth's  surface.  In  a  famous 
balloon  ascent  the  barometer 
fell  to  7  inches.  The  balloon 
was  then  about  7  miles  above 
sea  level,  and  had  left  more 
than  three  fourths  of  the  air 
behind.  When  a  barometer  is 
carried  down  into  a  deep  mine, 
the  mercury  column  rises, 
because  the  density  and  the 
pressure  of  the  air  are  greater 
there  than  at  the  surface.  FlG- 32- 

The  density  of  the  atmosphere  grows  less  as  we 
ascend. 

42.  Pumps. —  Pumps 

were  used  by  man  at  least  2,000  years  before  Torricelli 
showed  that  their  action  is  due  to  the  pressure  of  the 
atmosphere. 


15 


10 


42 


AIR  AND  FIRE 


If  we  put  the  open  end  of  a  pipe  under  the  water  of  a 
well  or  cistern,  and  remove  the  air  of  the  pipe,  the  atmos- 
pheric pressure  will  raise  the  water  into  the  pipe  about  34 
feet  (cf.  §  40).  In  other  words,  the  pipe 
and  the  well  become  a  water  barometer. 

The  simple  lift  pump  (Fig.  33)  not  only 
removes  the  air  from  the  pipe,  but  lifts  the 
water  to  the  spout.  It  consists  of  a  cylin- 
der in  which  a  tightly  fitting  piston  can  be 
moved  up  and  down  by  means  of  a  handle. 
The  cylinder  is  attached  to  a  pipe,  which 
extends  into  the  water. 

The  Lift  Pump.  In  the  bottom  of  the  cylinder  there  is  a  cylinder 

valve,  which  opens  upwards  so  as  to  admit  water 
from  the  pipe.  There  is  also  a  valve  in  the  piston.  This,  too,  opens 
upwards,  admitting  water  above  the  piston.  When  the  piston  is 
forced  downwards,  the  water  in  the  cylinder  opens  the  piston  valve 
and  closes  the  cylinder  valve.  Some  of 
the  water  of  the  cylinder  then  collects 
above  the  piston.  When,  now,  the  piston 
is  raised,  as  in  Fig.  33,  the  water  above  it 
closes  the  piston  valve,  and  the  water 
above  the  piston  is  discharged  through 
the  spout.  At  the  same  time  the  cylin- 
der valve  is  opened  by  the  water  below  it, 
and  more  water  is  forced  into  the  cylin- 
der. Thus  the  up  and  down  strokes  of 
the  piston  cause  a  more  or  less  regular 
discharge  of  water  from  the  spout. 

Force  Pumps  and  Rotary  Pumps. —  In 
the  force  pump  (Fig.  34)  the  piston  has 

no  valve.  When  the  piston  is  raised,  water  rises  into  the  pipe  and 
into  the  cylinder.  When  the  piston  descends,  the  water  below  it 
closes  the  cylinder  valve,  and  water  is  forced  out  through  the  discharge 


FIG.  34. 

A  Force  Pump  with  Its  Air 
Chamber. 


COMPRESSED  AIR 


43 


Discharge 


valve.  The  pressure  of  the  water  in  the  discharge  pipe  compresses 
the  air  in  the  air  chamber.  When,  now,  the  piston  is  raised  once 
more,  the  discharge  valve  is  closed  by  the  pressure  of  the  water  in 
the  discharge  pipe;  yet  the  stream  of  water  does  not  stop  flowing, 
because  of  the  pressure  of  the  air  in  the  air  chamber.  The  steam 
fire-engine  is  a  good  example  of  a  force  pump. 

A  rotary  pump  (Fig.  35)  consists  of  a  wheel  with  inclined  blades. 
The  wheel  is  turned  rapidly  by  an  engine,  and  removes  the  air  of  a 
pipe  dipping  into  water.  The 
water  is  then  raised  by  atmos- 
pheric pressure  into  the  case 
in  which  the  wheel  revolves. 
The  blades  of  the  wheel  force 
the  water  out  through  the  dis- 
charge pipe. 

Since  the  rotary  pump  has 
no  valves,  it  can  pump  water 
carrying  grit  and  dirt,  mate- 
rials which  would  clog  a  pump 
with  valves.  This  fact  makes 
it  especially  valuable  for  the 
draining  of  swamp  lands, 
marshes,  etc.,  and  for  pumping  into  canals  and  ditches  the  water 
that  is  to  be  used  in  irrigation,  the  artificial  watering  of  land. 

43.  Compressed  Air. — -While  an  ordinary  pump  re- 
moves air  from  a  given  space,  a  compression  pump  (cf. 
§  71)  packs  as  much  air  as  possible  into  a  given  space.  A 
bicycle  or  automobile  tire  pump  is  such  a  pump. 

When  compressed  air  is  released,  it  expands,  and,  like 
other  expanding  gases,  it  can  do  work  (cf.  §  24).  Thus, 
a  sand  blast  is  a  current  of  air  released  from  pressure,  and 
carrying  sharp  sand  with  great  speed.  If  the  sand  strikes 
glass,  it  chips  its  surface,  forming  ground  glass.  If  part 
of  the  glass  is  protected  with  wax,  while  the  rest  is  exposed 


take] 

I 

1  I 

Pulley 

FIG.  35. 

This  rotary,  or  centrifugal,  pump  is  driven  by  a 
•   belt  placed  over  the  pulley. 


44 


AIR  AND  FIRE 


to  the  blast,  a  design  will  be  made  on  the  glass.  The 
blast  is  used  to  clean  castings,  and  will  even  drill  holes  into 
steel. 

The  pneumatic  hammer  is  a  hammer  kept  in  rapid  motion  by  com- 
pressed air.  It  is  with  this  hammer  that  large  pieces  of  steel,  such  as 
those  of  bridges  and  of  the  framework  of  largeuil  bdings,  are  riveted 

together. 

compressed  ci.r  The    air    brake,    which 

stops  the  motion  of  trains, 
is  worked  by  compressed 
air  stored  in  the  locomo- 
tive. 

In  making  foundations 
for  bridges  and  buildings 
men  must  often  work  under 
water.  They  can  do  this 
by  going  down  in  large 
caissons,  or  diving  bells 
(Fig.  36).  Compressed  air 
is  forced  into  the  bell  at 
sufficient  pressure  to  keep 
the  water  from  rushing  in, 
and  to  give  fresh  air  to  the 
workmen.  The  used  air  bubbles  out  around  the  edge  of  the  bell. 

A  submarine  boat  is  supplied  with  compartments  which  can  be 
filled  with  water  when  the  boat  is  to  go  under  water.  The  boat  also 
carries  compressed  air  for  forcing  the  water  out  when  the  boat  is  to  rise 
to  the  surface. 

44.  Exercises. 

1.  What  is  the  volume  of  the  air  in  a  room  40  x  25  x  9  ft.?     Its 
weight  in  ounces?     In  pounds? 

2.  If  the  surface  of  a  man's  body  is  2,600  square  inches,  what  is  the 
pressure,  in  pounds,  of  the  atmosphere  upon  it?    Why  does  not  this 
weight  crush  the  body? 


Diving  Bell. 


FIG.  36. 
How  men  can  work  under  water. 


COLLECTION  OF  GASES 


45 


3.  If  an  elastic  balloon  holding  1  cu.  ft.  of  gas  at  the  earth's  surface 
were  to  ascend  until  the  barometer  height  is  15  in.,  would  the  volume 
of  the  gas  in  the  balloon  grow  smaller  or  larger?     Why? 

4.  Pouring  a  little  water  upon  the  piston  of  a  dry  pump  is  called 
"priming"  the  pump.    Why  does  this  help  the  action  of  the  pump? 

5.  Explain  why  you  can  ''suck"  lemonade  through  a  straw  or  other 
tube.     If  the  lemonade  had  the  density  of  water,  and  you  had  the 
necessary  strength,  how  high  could  you  suck  it? 


45.  Collection  of  Gases. — When  we  wish  to  collect  a 
gas  for  study,  we  must  remember  that  so-called  " empty7' 
vessels  are  filled 
with  air,  and  that 
to  fill  a  vessel  with 
another  gas  we 
must  have  some 
way  of  removing 
the  air.  One  way 
is  to  " sweep  out" 
the  air  by  passing 
the  other  gas 
through  the  vessel  for  some  time.  Fig.  37  shows  how 
we  might  fill  a  bottle  with  illuminating  gas  by  sweeping 
out  the  air.  We  must  use  a  large  excess  of  the  gas  to 
make  sure  no  air  remains. 


FIG.  37. 

Collecting  Gas  by  Displacement  of  Air  and  Air  by  Dis- 
placement of  Water. 


A  better  way  to  get  the  air  out  of  the  collecting  vessel  is  to  fill  the 
vessel  with  water.  Then  we  close  the  mouth  of  the  full  bottle  with  the 
hand,  or  with  a  piece  of  cardboard,  and  set  it,  upside  down,  in  a  pan  of 
water  (Fig.  37).  We  must  have  the  mouth  of  the  bottle  under  water 
before  we  uncover  it,  or,  as  we  well  know,  the  water  will  fall  out,  and 
air  will  take  its  place.  Now,  if  we  wish  to  collect  a  bottle  full  of  the 
air  from  the  lungs,  we  can  "blow"  through  a  tube  the  end  of  which  is 


46 


AIR  AND  FIRE 


placed  under  the  mouth  of  the  bottle  of  water.  The  air,  being  lighter 
than  water,  will  displace  the  water  of  the  bottle.  We  can  fill  a  bottle 
exactly  full  of  illuminating  gas  by  attaching  a  "delivery  tube"  to  the 
gas  outlet,  and  allowing  the  gas  to  displace  water  in  the  same  way. 

46.  Discovery  of  Oxygen. —  The  phenomenon  of  fire, 
or  burning,  has  fascinated  men  for  ages,  but  what  the  air 
has  to  do  with  it  no  one  understood  until  1774.  The 
explanation  was  given  by  Lavoisier,  a  French  scientist,  and 
was  as  important,  in  its  way,  as  the  explanation  of  gravity 
by  Newton  (cf.  §  18) ;  for  it  was  the  beginning  of  modern 
Chemistry.  Priestley,  an  English  experimenter,  had  just 
prepared  oxygen  (Aug.  1,  1774)  by  heating  a  red  powder 
which  we  now  call  mercuric  oxide. 


Sunlight 


Mercury 
Oxide 

Oxygen 


Priestley's  apparatus  (Fig.  38)  was  a  bottle  filled  completely  with 
mercury,  and  inverted  in  a  "bath"  of  the  same  liquid.    He  put  the 

mercuric  oxide  under  the  mouth  of  the 
bottle;  the  oxide,  being  lighter,  floated  to 
the  top  of  the  mercury.  He  then  brought 
sunlight  to  a  focus  (cf.  §  178)  upon  the 
mercuric  oxide  by  means  of  a  burning 
lens.  The  heat  produced  caused  the  red 
powder  to  disappear;  but  a  colorless  gas 
appeared  in  its  place.  When  Priestley  put 
into  the  gas  a  splinter  with  a  glowing  tip, 
the  spark  burst  into  flame.  He  also  put 
a  live  mouse  into  the  gas,  and,  to  his  sur- 
prise, it  continued  to  live.  Priestley  called 
the  gas  "good  air." 


FIG.  38. 

Priestley's  Way  of  Getting  Oxy- 
gen from  Mercury  Oxide. 


47.  The  Air  a  Mixture. — When  Lavoisier  heard  of 
Priestley's  discovery,  he  reasoned  that  the  gas  obtained 
by  Priestley,  which  supported  burning  and  life  so  much 


THE  AIR  A  MIXTURE 


47 


Mercury 


better  than  air,  must  be  present  in  the  air.  So  he  planned 
an  experiment  to  prove  that  he  was  right. 

Lavoisier  set  up  the  apparatus  shown  in  Fig.  39,  putting  some 
mercury  in  the  glass  retort.  The  drawn-out  tube  of  the  retort  was 
bent  so  that  it  dipped  into  the  pan  of  mercury.  Over  the  end  of  this 
tube,  and  dipping  below  the  mer- 
cury, was  the  bell  jar.  The  air  of 
the  bell  jar  and  of  the  retort  was 
thus  cut  off  from  the  outer  air, 
and  nothing  but  mercury  could 
get  into  the  apparatus.  Lavoisier 
then  heated  the  retort  for  12  days. 
Gradually  a  red  powder  collected 
on  the  mercury  in  the  retort.  At 
the  same  time  the  atmospheric 
pressure  pushed  some  mercury  into 
the  bell  jar.  This  showed  that  the 

volume  of  air  in  the  apparatus  became  smaller.  When  no  further 
change  took  place,  Lavoisier  let  the  apparatus  become  cool,  and  found 
that  only  4/5  of  the  air  remained.  The  air  that  was  left  "put  out"  a 
burning  candle,  and  mice  could  not  live  in  it.  So  Lavoisier  reasoned 
that  the  active  part  of  the  air  was  removed  by  the  heated  mercury,  and 
that  it  makes  up  about  1/5  of  the  air. 


FIG.  39. 

Lavoisier's  Experiment.   Heating  Mercury 
in  a  Confined  Portion  of  Air. 


When  Lavoisier  heated  the  red  powder  that  had  collected 
in  the  retort,  he  obtained  all  the  gas  that  had  been  lost 
by  the  air.  When  he  applied  to  this  gas  the  tests  which 
Priestley  had  used  for  his  "good  air/'  he  obtained  the 
same  results  as  Priestley.  Lavoisier  had  thus  proved  that 
the  air  consists  of  two  substances,  one  of  them  active, 
and  able  to  support  burning  and  life;  the  other,  inactive. 
The  active  gas  is  oxygen;  the  inactive  one,  nitrogen  (cf. 
also  §  54). 


48 


AIR  AND  FIRE 


48.  Burning  and  Oxidation. —  Many  metals  besides 
mercury  unite  with  the  oxygen  of  the  air.  Thus,  iron 
rusts  at  the  ordinary  temperature.  Hot,  melted  lead,  if 
stirred  so  that  a  fresh  surface  of  it  is  kept  exposed  to  the 
air,  is  gradually  changed  to  lead  oxide,  a  yellow  powder. 
Tin  is  changed  in  the  same  way  to  tin  oxide,  a  white  pow- 
der. Zinc  and  magnesium  burn  with  bright  flames  to  give 
their  oxides.  Powdered  magnesium  is  burned  to  give  the 
light  for  "flash  light "  photographs.  If  we  weigh  a 
quantity  of  any  one  of  these  metals,  and  then  weigh  the 

oxide  formed,  we  always  notice  a 
gain  in  weight;  this  is  due  to  the 
oxygen  that  is  taken  up  (Fig.  40) . 
The  uniting  of  a  substance  with 
oxygen  is  called  the  oxidation  of 
the  substance,  and  the  substance 
is  said  to  be  oxidized.  Burning 
is  also  called  combustion,  and  a 
substance  that  can  burn  in  the 
air  is  called  a  combustible  sub- 
stance. But  burning  is  not  differ- 
ent from  other  oxidation :  it  is  oxidation  which  is  so  rapid 
that  heat  and  light  are  given  off.  The  phenomenon  of 
burning  was  mysterious  for  so  long  a  time  because  the 
matter  of  a  burning  body  seems  to  be  destroyed.  This  is 
because  most  of  our  common  combustibles,  such  as  wax, 
coal,  wood,  and  paper,  give  invisible  gases  when  they  burn 
(Fig.  41).  Of  course  these  escaped  unnoticed  (cf.  §  38). 


FIG.  40. 

A  burning  body  takes  up  oxygen 
from  the  air,  and   gains  weight. 


49.  Flames. —  There  is   a   difference  in   the  way  in 
which  substances  burn:  some  have  a  large,  bright  flame; 


TO  PREPARE  OXYGEN  49 

while  others,  like  charcoal,  merely  glow.  The  explanation 
is  simple.  A  flame  is  a  burning  gas.  Substances  that  do 
not  give  off  gases  when  burning  do  not 
have  flames.  In  fact,  coke  and  charcoal 
are  the  material  that  is  left  when  the 
gaseous  part  of  coal  and  wood,  respec- 
tively, is  driven  off  by  heat  (cf.  §§117 
and  124). 

When  a  candle  burns  (Fig.  42),  a  little  of  the 
wick  is  consumed  in  melting  the  wax;  then  the  FIG.  41. 

melted  wax  is  drawn,  by  capillary  action  (cf.  §  32),       Burnis?ovea  °°al 
up  the  wick  into  the  flame.    The  heat  of  the  burn- 
ing wick  changes  the  liquid  wax  into  a  gas,  or  vapor,  and 
this  burns  with  a  flame,  producing  heat  and  light.    The 
flame  itself  is  merely  the  region  in  which  oxidation  is 
taking  place.     The  materials  burning  in  the  flame  are 
constantly  changing,  but  they  are  constantly  renewed; 
hence  the  flame  has  a  somewhat  definite  shape  and  size. 

50.  To  Prepare  Oxygen.—  Since  oxygen  is 
the  active  element  of  the  air,  we  cannot  pre- 
pare it  by  simply  removing  the  nitrogen.    We 
can,  however,  capture  the  oxygen  by  means 
of  some  such  substance  as  hqated  mercury  (cf.  §  47). 
By  heating  the  mercury  oxide  that  is  formed  to  a  higher 
temperature  we  can  get  the  oxygen  by  itself. 

Mercury  and  oxygen  (at  about  350°  C.)  give  mercury  oxide. 
Mercury  oxide  (at  about  380°  C.)  gives  mercury  and  oxygen. 

This  is  what  Lavoisier  actually  did. 
In  the  laboratory,  oxygen  is  generally  made  by  heating 
potassium  chlorate.     This  is  a  white  solid  which  melts 


50 


AIR  AND  FIRE 


FIG.  43. 
The  Common  Way  of  Preparing  Oxygen. 


when  heated,  and  foams,  or  "effervesces,"  as  the  oxygen 
passes  off.  If  a  small  amount  of  iron  oxide  (rust)  is  mixed 
with  the  potassium  chlorate  when  it  is  heated,  it  gives  off 

its  oxygen  more  easily. 
The  substance  manga- 
nese dioxide,  a  black 
solid,  has  the  same  effect. 

The  apparatus  required  for 
making  oxygen  is  shown  in 
Fig.  43.  A  test  tube  contains 
the  mixture  of  powdered  po- 
tassium chlorate  and  manga- 
nese dioxide.  The  delivery  tube  is  attached  "gas  tight"  to  the  test 
tube  by  means  of  a  rubber  stopper.  The  test  tube  is  then  heated 
with  a  very  small  flame,  and  the  oxygen  given  off  is  collected  over 
water  in  the  bottle.  When  the  bottle  is  full  of  oxygen,  it  is  stoppered, 
or  covered  with  a  glass  plate,  and  set,  right  side  up,  on  the  table. 

A  still  easier  method  of  mak- 
ing oxygen  is  to  let  a  solution  of 
hydrogen  peroxide  drop  into  a 
flask  (Fig.  44)  upon  some  crys- 
tals of  potassium  permanganate 
just  covered  with  water. 

51.  Properties  of  Oxy- 
gen.—  With  the  bottles  of 
oxygen  made  as  directed 
in  §  50  we  can  study  the 
properties  of  oxygen. 


Potassium  Permanganate 

and 
Dilute  Sulphuric  Acid 


FIG.  44. 
Another  Way  of  Preparing  Oxygen. 

(1)  In  the  first  place,  we  can 

test  a  bottle  with  a  glowing  splinter  (the  test  used  by  Priestley). 
(2)  Iron  does  not  burn  readily  in  air,  but  it  burns  in  oxygen.     This 
may  be  shown  as  follows  (Fig.  45): 


OXYGEN  AND  LIFE 


51 


FIG.  45. 

Burning  Iron  Wire  in 
Oxygen. 


Sand  is  put  into  one  of  the  bottles  of  oxygen,  so  that  the  bottom  is 
completely  covered.  Then  a  bundle  of  fine  iron  wires  (picture  cord) 
is  tipped  with  a  little  sulphur,  or  with  a  splinter  of  wood.  The  sulphur 
(or  wood)  is  lighted,  and  the  wire  is  put  into  the 
bottle  of  oxygen.  The  burning  tip  heats  the  iron 
to  its  "kindling  temperature,"  so  that  it  burns 
brilliantly  in  the  oxygen.  Iron  oxide  is  formed, 
as  in  rusting.  The  melted  oxide  collects  as  a  drop 
upon  the  end  of  the  wire,  or  falls  into  the  bottle. 
The  sand  is  used  to  protect  the  bottle  from  the 
hot  iron  oxide. 

(3)  Sulphur,  which  burns  with  an  almost  invis- 
ible, blue  flame  in  the  air,  burns  with  a  brilliant, 
violet  flame  in  oxygen.  The  sulphur  is  held  in  a 

"combustion  spoon"  (Fig.  46),  and  is  melted  and 
lighted  in  a  burner  before  being  put  into  the  oxygen. 
The  product  formed  is  sulphur  dioxide,  the  same 
choking  gas  that  results  when  sulphur  burns  in  air. 

(4)  Charcoal  burns  in  air  with  a  faint  glow;  but  in 
oxygen  it  burns  vigorously,  giving  off  a  brilliant  light. 
The  charcoal  is  held  by  means  of  a  copper  wire,  or  in  a 
combustion  spoon,  and  is  ignited  in  a  flame  before 
being  put  into  the  oxygen.    The  product  is  the  color- 
less gas,  carbon  dioxide.    If  we  put  "  lime  water  " 
(cf.  §  127)  into  the  bottle  in  which  charcoal  has  been 
burned,  the  lime  water  and  carbon  dioxide  unite  to  form  a  white, 
insoluble  solid  which  makes  the  lime  water  look  "milky."    In  a  bottle 
of  pure  oxygen  or  air,  lime  water  is  not  changed. 

Oxygen  dissolves  slightly  in  water.  Like  air,  of  which 
it  forms  a  part,  oxygen  has  no  color,  odor,  or  taste. 

52.  Oxygen  and  Life. —  Oxygen  forms  a  part  of  all 
living  things,  and  an  abundant  supply  is  needed  to  main- 
tain life.  The  process  of  getting  oxygen  in  contact  with 
the  tissues  of  an  animal  or  plant  is  called  respiration. 


FIG.  46. 

Burning  Sulphur 
in  Oxygen. 


52  AIR  AND  FIRE 

Respiration  consists  both  of  breathing,  which  is  performed 
for  the  higher  animals  by  lungs  (cf.  §  343),  and  also  of  the 
actual  oxidation  that  takes  place  throughout  the  body. 
A  grown  man  takes  in  (" inspires")  about  350  cubic  feet 
(10  cubic  meters)  of  air  in  a  day. 

The  purpose  of  respiration  is  to  get  the  oxygen  of  the 
air  to  combine  with  the  materials  of  the  body  that  are 
constantly  wearing  out,  and  to  oxidize  them  (cf.  §  48)  to 
substances  that  the  body  can  get  rid  of.  Since  this  worn- 
out  matter,  like  the  body  itself,  is  largely  made  up  of 
carbon  and  hydrogen,  it  is  changed  chiefly  to  carbon 
dioxide  and  water  when  oxidized  (cf.  §§51  and  105).  The 
oxidation  within  the  body  is  not  an  actual  burning;  but 
it  produces  heat.  This  heat  keeps  the  bodies  of  animals 
warm.  In  man  the  normal  temperature  is  98.6°  Fahren- 
heit, or  37°  Centigrade  (cf.  §  63).  In  certain  diseases  the 
lungs  are  not  able  to  get  oxygen  rapidly  enough  from  the 
air;  so  pure  oxygen  is  used. 

Water  animals  depend  upon  the  oxygen  dissolved  in 
natural  water.  Fishes,  clams,  etc.,  take  in  oxygen  through 
their  gills  (cf.  §§  337  and  341).  In  the  gills  the  same  ex- 
change of  carbon  dioxide  for  oxygen  takes  place  as  in  the 
lungs  of  higher  animals. 

53.  Exercises. 

1.  How  can  you  show  that  the  expired  breath  contains  water? 
Carbon  dioxide? 

2.  Give  the  dates  of  the  birth  and  the  death  of  Priestley  and  of 
Lavoisier.    What  did  each  do  for  science?     (See  Glossary.) 

3.  What  substance  is  used  to  polish  stoves  (cf.  §  119)?    How  does 
it  prevent  rusting?    What  other  materials  are  used  to  cover  iron  to 
prevent  rusting? 


HOW  NITROGEN  IS  PREPARED 


53 


4.  Why  do  we  use,  first,  paper,  then  wood,  and  then  coal  in  starting 
a  coal  fire? 

5.  Why  are  oxides  used  as  fire-proofing  materials? 

6.  Compare  the  composition  of  the  air  that  enters  at  the  bottom  of 
a  stove  with  that  which  passes  out  into  the  flue. 

7.  Why  does  a  kerosene  lamp  need  a  wick?    Why  a  chimney? 

8.  Why  does  a  blanket  or  rug  put  out  a  fire?    Why  does  water? 

9.  When  a  gas  is  collected  over  water,  why  does  the  gas  force  the 
water  out  of  the  bottle? 


54.  How  Nitrogen  is  Prepared. —  One  method  of  pre- 
paring nitrogen  is  to  remove  the  oxygen  from  air.  We 
may  remove  the  oxygen,  as  Lavoisier  did,  by  means  of 
heated  mercury;  but  an  easier 
way  is  to  burn  phosphorus  in  a 
bottle  or  jar  of  air  (Fig.  47). 

A  small  heap  of  red  phosphorus  is 
placed  in  the  middle  of  a  thin  slice  cut 
from  a  cork  about  three  fourths  of  an 
inch  in  diameter.  A  wire  pushed  into 
tfye  cork  supports  it.  To  hold  the  wire 
upright,  we  stick  it  into  a  rubber  stop- 
per, placed,  large  end  downward,  on  the  bottom  of  a  pan  of  water. 
The  water  is  about  two  inches  deep.  The  phosphorus  is  lighted,  and 
the  jar  of  air  (a  fruit  jar  does  very  well)  is  immediately  placed  over 
the  burning  phosphorus,  and  pressed  tightly  against  the  bottom  of 
the  pan.  After  the  phosphorus  has  burned  for  a  moment,  the  hand 
may  be  removed.  Water  rises  into  the  jar  to  take  the  place  of  the 
oxygen  used  up. 

The  white  smoke  is  phosphorus  oxide.  The  jar  is  left  until  the 
smoke  has  entirely  disappeared  (it  dissolves  in  the  water) ;  then  a  piece 
of  glass  or  cardboard  is  slipped  under  the  jar,  and  the  jar  is  set  upright 
on  the  table.  A  burning  splinter  "goes  out"  when  put  into  the  jar. 
If  too  many  bubbles  did  not  escape  when  the  jar  was  put  over  the 


FIG.  47. 

Burning  Phosphorus  in  a  Jar  of  Air 
Over  Water  leaves  Nitrogen. 


54  AIR  AND  FIRE 

phosphorus,  the  volume  of  water  that  enters  the  jar,  and,  therefore, 
the  volume  of  the  oxygen,  will  be  about  one  fifth  of  the  volume  of  air  in 
the  jar  at  first. 

Nitrogen  made  in  this  way  contains  argon,  a  gas  even  more  inactive 
than  nitrogen  itself.  Argon  makes  up  almost  one  per  cent,  by  volume, 
of  air. 

Perhaps  the  most  convenient  way  to  get  a  250  c.c.  bottle 
of  nitrogen  is  to  heat  carefully  a  solution  of  5  g.  of  sodium 
nitrite  and  5  g.  of  ammonium  chloride  in  100  c.c.  of  water. 
The  nitrogen  escapes,  and  is  collected  over  water. 

55.  Properties  of  Nitrogen. —  Unlike  oxygen,  nitrogen 
does  not  unite  readily  with  other  substances,  and  does 
not  support  burning  and  life.     It  dilutes  the  active  oxygen 
of  the  air.    Nitrogen  is  somewhat  lighter  than  the  air, 
and  is  very  slightly  dissolved  by  water.    Like  oxygen,  it  is 
colorless,  tasteless,  and  odorless. 

Nitrogen  finds  it  hard  not  only  to  unite  with  other 
substances,  but  also  to  hold  its  place  in  many  substances 
that  contain  it.  As  a  result  of  this  property  it  is  made  a 
part  of  all  our  common  explosives,  such  as  gunpowder, 
nitroglycerine,  guncotton,  etc.  These  are  all  substances 
that  hold  nitrogen  loosely.  When  the  explosive  is  set  on 
fire,  or  is  given  a  "shock"  (cf.  §  24),  the  nitrogen  is  set 
free  as  a  gas  under  great  pressure,  and  in  expanding  does 
the  work  required  of  the  explosive. 

56.  Nitrogen  and  Life. —  The  properties  and  uses  of 
nitrogen  described  in  preceding  sections  are  due  to  the 
fact  that  it  has  little  activity,  or  little  power  of  uniting 
with  other  substances.     But  nitrogen  is  important  also 
because  of  certain  positive  qualities:  it  forms  a  necessary 


NITROGEN  AND  LIFE 


55 


part  of  proteids,  or  albumins,  materials  needed  by  all 
living  cells.  Nitrogen  is,  therefore,  a  necessary  part  of 
all  animals  and  plants.  The  proteids  make  up  a  large 
part  of  such  food  as  meat,  eggs,  cheese,  and  milk. 

Animals  cannot  make  their  own  proteid;  they  must  get 
it  by  feeding  upon  plants.  Plants  make  proteids  out  of  the 
carbon,  hydrogen,  oxygen,  nitrogen,  etc.,  which  they  ob- 
tain from  the  soil  and  the  air.  Now,  most  plants  can  take 
up  nitrogen  only  when  it  is  a  part  of  certain  compounds 
dissolved  in  the  water  of  the  soil.  Hence  soils  must  con- 
tain nitrogen  compounds  to  be  fertile. 


While  most  plants  can  make  proteids  only  out  of  nitrogen  com- 
pounds present  in  soil,  some  plants  seem  to  take  up  nitrogen  directly 
from  the  air.  Such  are  beans,  peas,  clover,  and  alfalfa.  It  has  been 
found  that  the  plants  named  have  this  power  because  " colonies"  of 
bacteria  —  very  small  plants  (cf.  §  324)  — 
find  a  home  upon  their  roots.  It  is  the 
bacteria  that  take  the  nitrogen  out  of  the 
air,  and  build  it  into  the  complex  albumins 
upon  which  the  beans,  etc.  feed.  But  the 
bacteria  produce  not  only  enough  proteid 
for  the  beans,  etc.,  but  they  produce  an 
excess  of  it,  and  leave  it  in  the  soil.  Be- 
cause they  themselves  contain  so  much 
proteid,  beans,  peas,  and  clover  are  valu- 
able as  food  for  man  and  animals;  but 
they  are  even  more  important  because 
they,  or,  rather,  the  bacteria  growing 
upon  them,  are  the  means  of  bringing  into 

a  soil  the  nitrogen  it  needs  for  other  plants.  As  all  farmers  know, 
clover  is  grown  in  a  field,  and  " ploughed  under,"  to  enrich  the  soil 
for  crops  of  grain.  Artificial  fertilizers,  containing  nitrogen  com- 
pounds, are  often  added  to  the  soil  for  the  same  purpose. 


TUBCffCLE 


FIG.  48. 

A  Clover  Plant  with  its 
Tubercles. 


56 


AIR  AND  FIRE 


FIG.  49. 

A    Dewar    Bulb 
for    Holding 
Liquid  Air. 


57.  Liquid  Air. —  In  the  liquid  form  air  is  colorless, 
and  has  about  the  same  density  as  water.  It  is  composed 
of  liquid  oxygen  and  nitrogen.  Liquid  air  is  constantly 
evaporating;  to  prevent  explosions  we  keep 
it  in  open  vessels  called  "Dewar  bulbs," 
from  the  inventor  (Fig.  49).  They  have 
double  walls,  and  the  air  is  removed  from  the 
space  between  the  walls,  so  that  heat  from 
the  outside  cannot  affect  the  liquid  within. 
The  walls  of  the  bulbs  are  silvered  for  the 
same  reason.  "Thermos"  and  "Caloris" 
bottles  are  made  on  the  principle  of  Dewar 
bulbs,  to  keep  a  cold  liquid  from  getting  warm  and  a  hot 
liquid  from  getting  cool  (cf.  Ex.  12,  §  68).  Air  is  made 
liquid  at  a  low  temperature  by  great  pressure.  It  boils 
at  about  -190°  C.  (Fig.  50). 

Alcohol  held  in  liquid  air  becomes  solid,  like  ice.  Mercury  is 
changed  to  a  hard  metal,  and  may  be  used  as  a  hammer  head,  to  drive 
nails.  A  rubber  ball  put  into  liquid  air  be- 
comes brittle,  and  flies  into  fragments  when 
thrown  on  the  floor.  A  piece  of  meat  be- 
haves in  the  same  way.  Liquid  air  that 
actually  wets  the  skin  burns  it  like  white- 
hot  iron;  yet  the  hand  may  be  put  into  the 
liquid  for  a  moment  without  injury,  because 
a  layer  of  gaseous  air  covers  the  hand  like  a 
glove. 


FIG.  50. 


Liquid  Air  Boiling 
on  Ice. 


58.  How  the  Atmosphere  is  Puri- 
fied.—  Since  the  air  receives  impurities  from  the  breathing 
of  animals  and  plants,  from  all  burning,  and  from  all 
decay,  why  does  it  not  become  foul,  and  unfit  to  breathe? 


HOW  THE  ATMOSPHERE  IS  PURIFIED  57 

The  answer  is  that  the  impurities  are  constantly  being 
removed.  The  wind  scatters  foul  air,  and  mixes  it  with 
fresh  air  from  the  country,  the  mountains;  and  the  sea. 
The  rain  washes  out  impure  gases,  dust,  smoke,  and 
bacteria,  or  germs.  Sunlight  destroys  many  bacteria  that 
produce  disease.  Other  bacteria  bring  about  the  oxida- 
tion of  dead  organic  matter,  and  so  destroy  it.  Plants 
use  up  the  carbon  dioxide  cast  off  by  animals,  and  give 
back  oxygen  in  its  place  (cf.  §  309). 

59.  Summary. — The  atmosphere  is  the  gaseous  ocean  that  forms 
the  outer  layer  of  the  earth.  Air  is  the  substance  that  makes  up  the 
atmosphere. 

Air  is  matter,  for  it  takes  up  space,  and  has  weight,  inertia,  etc. 

The  pressure  of  the  atmosphere  is  due  to  the  weight  of  the  air.  It 
is  measured  by  the  barometer,  and  is  equal  to  about  15  Ibs.  for  each 
square  inch  of  surface  at  sea  level.  The  pressure  becomes  less  as  we 
go  up  a  mountain,  and  greater  as  we  go  down  into  a  mine. 

The  lift  pump  is  a  device  for  removing  the  air  that  is  over  a  liquid, 
so  that  atmospheric  pressure  will  raise  the  liquid.  Its  limit  is  about 
34  feet  for  water,  and  30  inches  for  mercury. 

Compressed  air,  like  other  compressed  gases,  can  do  work  when  it 
expands. 

Gases  are  "  collected  "  by  displacement  of  air  or  water. 

Priestley  discovered  oxygen  in  1774  by  heating  mercury  oxide. 

Lavoisier  proved  that  air  consists  of  two  substances,  oxygen  and 
nitrogen. 

Oxygen  makes  up  about  one  fifth,  by  volume,  of  air. 

Burning  in  air  is  union  with  oxygen,  or  oxidation.  Oxidation  may 
be  slow,  as  in  rusting  and  decay,  or  rapid,  as  in  burning. 

A  flame  is  a  burning  gas. 

Oxygen  is  prepared  by  heating  mercury  oxide  or  a  mixture  of 
potassium  chlorate  and  manganese  dioxide,  or  by  putting  hydrogen 
peroxide  with  potassium  permanganate. 

Oxygen  is  colorless,  tasteless,  odorless,  and  slightly  soluble  in  water. 


58  AIR  AND  FIRE 

Bodies  that  burn  slowly  in  air  burn  vigorously  in  oxygen.  Oxygen  is 
a  part  of  all  living  things. 

Respiration  consists  of  breathing  and  of  oxidation.  The  heat  pro- 
duced in  the  oxidation  keeps  the  body  warm.  Water  animals  use  the 
oxygen  that  is  dissolved  in  water. 

Nitrogen  is  made  from  air  by  removing  the  oxygen.  It  is  also  made 
by  heating  a  solution  containing  ammonium  chloride  and  sodium 
nitrite. 

Nitrogen  is  colorless,  tasteless,  odorless,  lighter  than  oxygen,  and 
inactive. 

Nitrogen  is  held  loosely  in  many  substances,  and  is  set  free  from 
most  explosives. 

Nitrogen  is  necessary  to  life,  since  it  is  a  part  of  proteids.  Proteids 
are  made  by  plants. 

Clover,  beans,  etc.,  support  colonies  of  bacteria  that  make  proteids 
out  of  nitrogen  and  other  materials. 

Liquid  air  is  a  mixture  containing  liquid  nitrogen  and  liquid  oxygen. 
Most  substances  change  their  properties  when  exposed  to  it,  owing 
to  its  low  temperature. 

The  atmosphere  as  a  whole  does  not  become  unfit  for  breathing 
because  of  the  winds,  ram,  sunlight,  oxidizing  bacteria,  and  plants. 

60.  Exercises. 

1.  How  can  you  tell  a  bottle  of  air  from  one  of  oxygen?    One  of  air 
from  one  of  nitrogen?    One  of  nitrogen  from  one  of  carbon  dioxide? 

2.  What  gases  do  plants  take  from  the  air?    Animals?    What  gas 
does  each  restore  to  the  air? 

3.  If  the  cover  of  a  fruit  jar  has  an  area  of  5  square  inches,  and  the 
jar  is  empty  (a  vacuum),  how  great  a  weight  must  I  lift  to  get  the  cover 
off,  not  counting  friction? 

4.  Why  does  the  air  seem  so  refreshing  after  a  rain  or  a  snowfall? 
Why  should  sunlight  and  air  be  admitted  into  the  rooms  in  which  we 
live? 


0 

Fio.  51. 

Metal  Ball  and 

Ring. 


CHAPTER  IV 

HEAT 

61.  Heat  and  Matter. —  It  is  a  familiar  fact  that  most 
bodies  increase  in  volume  as  they  grow  hot,  and  shrink  as 
they  grow  cold.  Thus,  a  brass  or  iron  ball  (Fig. 
51)  which  just  goes  through  a  ring  when  cold 
will  not  go  through  it  when  hot.  If,  however, 
the  ring,  as  well  as  the  ball,  is  heated,  then  the 
ball  will  go  through  it.  A  liquid,  like  water  or 
mercury,  which  just  fills  a  flask  at  the  tem- 
perature of  the  room, 'overflows  when  heated, 
but  does  not  fill  the  flask  when  cooled.  A  gas 
behaves  in  the  same  way.  Thus,  if  a  flask  of 
air  is  heated  (Fig.  52),  some  of  the  air  escapes;  but  the 
volume  of  the  air  contracts  when  the  flask  is  cooled. 

How  can  we  explain 
these  changes  of  volume? 
It  is  hard  to  see  how  the 
volume  of  a  body  can 
change  unless  the  matter 
of  the  body  is  broken  up 
into  particles,  with  spaces 
between  them.  Then, 
if  the  volume  becomes 
smaller,  as  is  the  case 
when  a  body  is  cooled,  we 

Heating  expands  air"  cooling  makes  it  shrink.     Can  explain  the  shrinkage 


FIG.  52. 


60  HEAT 

by  saying  that  the  particles  are  crowded  closer  together. 
Scientists  believe  that  matter  really  consists  of  such 
particles,  and  call  them  molecules,  or  "  little  masses." 
The  molecules  are  believed  to  be  in  motion.  Each 
molecule  needs  a  portion  of  space  in  which  to  move 
about;  hence  the  volume  of  a  body  is  the  sum  of  the 
spaces  needed  by  all  the  molecules,  in  addition  to  the  vol- 
umes of  the  molecules  themselves. 

The  motion  of  the  molecules  is  heat.  When  we  add  heat  to  a  body, 
each  molecule  moves  more  rapidly,  and  pushes  its  neighbors  farther 
away.  Because  of  this  the  distance  between  molecules  becomes 
greater,  and  the  volume  of  the  body  increases.  We  assume  that 
when  bodies  expand  and  contract  the  volumes  of  the  molecules  remain 
unchanged. 

The  molecules  are  very  small.  Scientists  estimate  the  number  of 
molecules  in  1  c.c.  of  a  gas  as  about  27  million  million  millions  (27,000,- 
000,000,000,000,000). 

62.  Thermometers. —  We  make  use  of  the  expansion 
and  contraction  of  matter  in  the  thermometer,  the  instru- 
ment with  which  we  measure  temperature.  The  common 
thermometer  consists  of  a  glass  tube  having  a  bulb  at  one 
end.  The  bulb  and  part  of  the  tube  contain  mercury. 
The  inside  of  the  tube  is  of  a  very  small  bore,  so  that  if 
the  mercury  expands  only  a  very  little  in  the  bulb,  it  will 
make  a  great  difference  in  the  length  of  the  mercury 
"thread"  inside  the  tube.  Glass  expands  when  heated, 
as  well  as  mercury,  but  only  y7as  much;  hence  the  ex- 
pansion we  see  in  a  thermometer  is  the  difference  between 
the  expansion  of  mercury  and  that  of  glass. 

When  a  thermometer  is  made,  the  end  of  the  tube  is  open,  and  there 
is  enough  mercury  to  fill  the  bulb  and  a  little  of  the  tube.  The  instru- 


THE   TWO   THERMOMETER   SCALES 


61 


ment  is  then  heated,  so  that  bulb  and  tube  are  completely  filled,  and 
the  open  end  is  sealed  by  melting  the  glass. 

The  thermometer  is  then  graduated,  that  is,  the  "degree"  marks  are 
put  on  it.  First  the  bulb  is  put  into  melting  ice 
(Fig.  53),  and  the  point  at  which  the  mercury  comes 
to  rest  is  marked  the  freezing  point.  Then  water 
is  made  to  boil  under  " standard  pressure"  (cf.  §  40), 
and  the  bulb  is  put  into  the  steam  that  comes  off 

(Fig.  54).     The  place  at  which 

the  mercury  stops  is  called  the 

" boiling    point"    mark    of    the 

thermometer. 


FIG.  53. 

Getting  the  Freezing 
Point  of  a  Ther- 
mometer. 


FIG.  54. 

Getting  the  Boiling 
Point  of  a  Ther- 
mometer. 


63.  The  Two  Thermom- 
eter Scales. —  The  differ- 
ence between  the  two  common  thermom- 
eters —  the  Fahrenheit  and  Centigrade 
thermometers — is  in  the  number  of  de- 
grees that  are  put  between  the  freezing 
point  mark  and  the  boiling 
The  maker  of  the  Centigrade 
He  divided  the  space 


point  mark, 
instrument  was  Celsius. 

between  the  two  marks  into  100  degrees  (Fig. 
55).  "Centigrade"  means  just  that:  "100 
degrees"  or  "steps."  Celsius  made  the  freez- 
ing point  of  his  thermometer  0°,  and  the 
boiling  point  100°.  If  the  thermometer  tube 
is  of  the  same  bore  throughout,  and  a  new 
mark  is  made  as  far  above  100°  as  0°  is  below 
it,  the  new  mark  will  be  200°.  In  this  way 
the  other  marks  of  the  thermometer  are  fixed. 

The  Fahrenheit  thermometer  is  named  from  The  Fahrenheit 
its  maker,  who  took  for  his  0°  the  temperature   lcfi£entigrade 


62  HEAT 

produced  by  a  certain  "freezing  mixture"  (cf.  §  93).  The 
melting  point  of  ice,  on  the  Fahrenheit  thermometer,  is 
32°,  and  the  boiling  point  of  water  212°. 

The  number  of  degrees  between  32°  and  212°  is  180;  consequently 
100  Centigrade  degrees  equal  180  Fahrenheit  degrees.  Each  Fahren- 
heit degree  is,  therefore,  5/9  of  a  Centigrade  degree,  and  each  Centi- 
grade degree  is  9/5  of  a  Fahrenheit  degree.  If  we  multiply  the  number 
of  degrees  shown  by  a  Centigrade  thermometer  by  9/5,  and  then  add 
32,  we  get  the  Fahrenheit  reading. 
Fahr.  =  (Cent.X9A)+32. 

If  we  subtract  32  from  the  Fahrenheit  reading,  and  then  multiply 
the  remainder  by  8/9,  we  get  the  Centigrade  reading. 
Cent.  =  5/9(Fahr.  —  32) . 

The  Centigrade  scale  is  used  almost  everywhere  on  the  continent  of 
Europe,  and  practically  everywhere,  the  world  over,  for  scientific 
work.  For  temperatures  below  —  39.1°  C.,  such  as  are  found  in  the 
Arctics,  alcohol  is  used  instead  of  mercury  (cf.  §  57). 

64.  Temperature  and  Heat. —  We  must  know  the 
difference  between  quantity  of  heat  and  degree  of  heat. 
We  know  whether  a  body  is  hot  or  cold,  generally  speak- 
ing, by  its  degree  of  heat,  that  is,  its  temperature.  The 
temperature  of  a  body  depends  upon  the  rapidity  with 
which  its  molecules  are  moving,  and  not  upon  whether 
there  are  many  molecules  or  few.  But  the  heat  which  a 
body  possesses  depends  upon  the  speed  of  the  molecules 
and  also  upon  the  number  of  molecules,  that  is,  upon  both 
the  temperature  of  the  body  and  its  mass.  We  shall  see 
later  (§  73)  that  it  also  depends  upon  the  substance  of 
which  the  body  is  composed. 

The  unit  of  heat  quantity  is  called  a  calorie,  just  as  the  unit  of  mass 
is  called  a  gram.  A  calorie  is  the  amount  of  heat  needed  to  warm 
1  gram  of  water  1°  C.  It  is  also  the  amount  given  off  by  1  g.  of  water 


CONVECTION  63 

when  its  temperature  falls  1°  C.  So  1  g.  of  water  in  cooling  from  100° 
C.  to  0°  C.  gives  off  100  calories  of  heat.  The  same  amount  is  given 
off  when  2  g.  of  water  are  cooled  from  50°  C.  to  0°  C.,  and  when  10  g. 
are  cooled  from  10°  C.  to  0°  C. 

65.  Ways   of   Distributing  Heat;   Conduction. —  If  a 

flat-iron  is  placed  on  a  stove,  the  iron  becomes  warm, 
because  heat  (motion  of  molecules)  from  the  stove  is 
given  to  it.  If  you  touch  the  flat-iron,  it  gives  some  of 
its  heat  to  the  hand;  hence  the  iron  feels  warm.  The  heat 
has  been  conducted,  first  from  the  stove  to  the  flat-iron, 
then  from  the  flat-iron  to  your  skin.  But  if  you  hold  a 
piece  of  ice  in  your  hand,  the  hand  becomes  cold,  because 
heat  is  conducted  from  your  hand  to  the  ice.  So  the 
objects  you  handle  are  either  hot  or  cold  according  as 
they  give  heat  to  the  hand,  or  take  it  from  the  hand. 

The  handle  of  a  flat-iron  can  still  be  held  comfortably  after  the 
bottom  is  hot;  but  in  a  short  time  the  handle,  also,  is  heated  by  con- 
duction from  the  part  nearer  the  stove.  To  hold  it  then,  we  use  a  non- 
conducting handle  of  cloth  or  of  wood.  It  would  take  longer  to  heat 
a  brick  from  the  bottom  to  the  top,  because  it  is  a  poorer  carrier,  or 
conductor,  of  heat.  Metals  are  the  best  heat  conductors;  air  is 
probably  the  poorest.  Water,  wood,  and  paper  are  poor  conductors. 
Conduction  is  only  one  of  the  ways  in  which  heat  is  distributed;  other 
ways  are  by  radiation  and  by  convection. 

66.  Radiation. —  If  you  stand  near  a  stove,  you  become 
warm  without  touching  the  stove.     Heat  is  radiated  to 
you  from  the  stove.    If  you  are  near  a  block  of  ice,  you 
become  chilled,  because  your  body  is  radiating  heat  to  the 
ice.    Heat  reaches  the  earth  from  the  sun  by  radiation 
through  space. 

67.  Convection. —  Convection  is  not  really  a  new  way 


64 


HEAT 


of  distributing  heat,  but  depends  on  the  other  two  ways. 
The  air  near  a  stove  becomes  heated  by  conduction  and 
radiation.  As  a  result  it  expands,  and  becomes  lighter. 
While  a  cubic  foot  of  air  at  32°  F.  (0°  C.)  weighs  about  1.2 
oz.,  at  80°  F.  (27°  C.)  it  weighs  1.1  oz.  The  lighter  air 
then  rises  to  make  room  for  the  cooler 
air,  which  flows  in  to  take  its  place 
(Fig.  222,  §  274) .  Thus  ' '  convection 
currents "  are  set  up,  and  the  air 
rises  while  it  is  warm  and  descends 
again  when  it  has  become  cooled. 

' '  Hot  air  "  furnaces  heat  our  houses 
(Fig.  56)  because  the  warmed  air 
flows  upward  through  the  "registers  " 
to  make  room  for  the  cold  air  taken 
in  at  the  bottom  of  the  furnace  (' '  cold 
air  intake"  ;c/.  §248). 


Fio.  56. 

Convection  Currents  from 
a  Furnace. 


When  air  is  cooled,  convection  currents  are  also  set  in  motion. 
Because  of  its  greater  density  the  cold  air  falls,  and  warm  air  flows  in 
to  take  its  place.  Hence  in  ice-boxes  (Fig.  57)  the  waste  water  is  not 
allowed  to  drop  directly  into  the  air,  but  is  controlled  by  a  "trap" 

which  permits  only  the  waste  water,  and  not 

the  cold  air,  to  flow  out  at  the  bottom  of  the 
refrigerator. 

Convection  currents  can  also  be  seen 
when  a  liquid  is  heated  and  cooled,  if  bits 
of  paper  or  sawdust  are  put  into  the 
liquid.  Hot  water  heating  of  houses  de- 
pends upon  such  currents  (cf.  §  243). 
Convection  currents,  and  the  fact  that  water 
is  most  dense  at  4°  C.,  prevent  the  freezing 
of  lakes  and  rivers  except  near  the  surface 
(cf.  §  87). 


FIG.  57. 

Trap  in  an  Ice-Box,  to  Pre- 
vent Cold  Air  from 
Falling  Out. 


PHYSICAL  STATES  OF  MATTER  65 

68.  Exercises. 

1.  When  the  glass  stopper  of  a  bottle  "sticks,"  we  can  often  loosen 
it  by  heating  the  neck  of  the  bottle.    Why? 

2.  If  you  heat  water  in  a  thick  glass  bottle  over  a  flame,  the  bottle 
usually  breaks,  while  a  thin  glass  flask  does  not.    Why? 

3.  Why  do  telephone  wires  sag  in  summer  and  become  taut  in  winter? 

4.  Alcohol  boils  at  78°  C.;  what  temperature  is  this  on  the  Fahren- 
heit scale?    The  room  temperature  is  70°  F. ;  what  is  this  on  the 
Centigrade  scale? 

5.  How  could  you  make  an  air  thermometer,  that  is,  one  using  the 
expansion  of  air  instead  of  that  of  mercury? 

6.  Which  feels  colder  in  a  room,  oilcloth  or  carpet?    Wood  or 
metal?    Is  there  any  real  difference  of  temperature?    Explain. 

7.  Why  can  ice  cream  be  carried  in  a  paper  box  through  heated  air, 
and  yet  not  melt?    Would  a  tin  box  be  better? 

8.  Which  feels  hotter,  the  handle  of  a  silver  spoon,  or  that  of  an 
iron  spoon,  if  the  bowl  of  each  is  in  boiling  water?    Why? 

9.  Why  does  air  enter  a  stove  at  the  bottom,  and  go  out  at  the  top? 

10.  Where  should  steam  pipes  be  put  to  heat  a  room?    Where 
should  pipes  of  cold  water  be  placed  in  a  cold  storage  room  in  order  to 
cool  the  room? 

11.  Why  are  houses  built  with  double  walls  having  air  spaces  be- 
tween them? 

12.  How  is  a  "fireless  cooker"  made?    Why  is  the  heat  not  given 
off?    How  is  it  like  a  Thermos  bottle  (cf.  §  57)? 

69.  Physical  States  of  Matter;  Solids. —  If  we  believe 
that  matter  is  broken  up  into  molecules  (§  61),  we  can 
understand  the  differences  between  solids,  liquids,  and 
gases,  the  three  physical  states,  or  forms,  of  matter.    The 
two  causes  at  work  upon  the  molecules  are  cohesion  and 
heat.    Cohesion  represents  the  attraction  of  the  molecules 
for  one  another;  heat  is  the  motion  of  the  molecules. 
Cohesion  draws  the  molecules  together;  heat  causes  them 
to  fly  apart. 


66  HEAT 

In  a  solid,  like  ice  or  sulphur,  the  cohesion  between  the 
molecules  greatly  overbalances  the  motion  of  the  mole- 
cules; therefore  a  solid  has  a  definite  form.  Usually  a 
solid  forms  crystals  (cf.  §  95). 

When  solids  are  melted,  their  temperature  does  not 
rise  during  the  melting;  but  the  heat  added  is  used  up  in 
overcoming  cohesion.  Thus,  when  ice  at  0°  C.  is  brought 
into  a  room  at  the  ordinary  temperature,  the  ice  melts; 
but  its  temperature  remains  0°  C.  until  all  of  the  ice  is 
melted.  If  the  ice  and  the  water  formed  by  its  melting 
are  stirred  thoroughly,  the  temperature  of  the  water  also 
remains  0°  C.  until  the  ice  disappears.  The  reason  is  that 
the  heat  which  the  ice  receives  from  the  room  is  used  up 
in  melting  the  ice  instead  of  in  raising  the  temperature  of 
the  water  or  the  ice. 

To  change  a  gram  of  ice  at  0°  G.  to  water  at  0°  G.  requires  as  much 
heat  as  to  warm  a  gram  of  water  from  0°  C.  to  80°  C.,  that  is,  80  calories 
of  heat. 

All  the  heat  taken  up  by  ice  in  melting  is  given  off  again  when  water 
freezes.  The  heat  that  is  given  off  by  tubs  of  freezing  water  is  used  to 
keep  vegetables  from  freezing.  The  temperature  in  the  vegetable 
cellar  cannot  fall  much  below  0°  C.  until  all  the  water  is  frozen.  The 
vegetables  themselves  do  not  freeze  at  0°  C. 

70.  Liquids. —  We  know  that  liquids  are  different  from 
solids  in  one  important  way:  they  have  no  definite  shape, 
but  take  the  shape  of  the  vessel  that  holds  them.  We 
explain  this  by  saying  that  the  heat,  or  motion,  of  the 
molecules  of  a  liquid  is  greater  than  in  the  case  of  a  solid; 
so  that  cohesion  cannot  keep  the  liquid  molecules  in  any 
particular  order  or  arrangement. 

Most  liquids  contract,  or  grow  smaller  in  volume,  when 


GASES  67 

they  freeze.  Water  is  an  exception:  100  c.c.  of  water  at 
0°  C.  become  109  c.c.  of  ice  at  0°  C.  On  this  account  water 
pipes  often  burst  in  winter,  and  water  that  freezes  in  the 
cracks  of  rocks  breaks  the  rocks  in  pieces  (cf.  §  289). 

Metals  that  have  about  the  same  volume  when  solid  as 
when  liquid  can  be  used  to  make  castings;  for  the  casting 
will  then  fill  the  mold  completely.  Cast  iron,  type  metal, 
and  brass  are  metals  of  this  sort.  But  gold  and  silver, 
which  shrink  when  they  become  solid,  cannot  be  cast; 
they  must  be  stamped,  or  "  minted." 

When  a  liquid  becomes  a  gas,  or  vapor,  an  enormous  increase  in 
volume  takes  place.  Thus,  1  c.c.  of  water  at  100°  C.  becomes  about 
1,200  c.c.  of  steam  at  100°  C.  Engineers  express  this  by  saying,  "A 
cubic  inch  of  water  gives  a  cubic  foot  of  steam." 

The  heat  taken  up  in  changing  a  gram  of  water  at  100°  C.  to  steam 
at  100°  C.  is  536  calories  (cf.  §  64).  The  same  amount  of  heat  is  set 
free  when  a  gram  of  steam  at  100°  C.  is  condensed  to  water  at  100°  C. 
Hence  a  scalding  from  steam  is  much  more  painful  than  one  from  hot 
water. 

When  a  liquid  is  evaporating  rapidly,  it  is  always  a  little  colder  than 
the  surrounding  air.  In  tropical  countries  people  take  advantage  of 
this  fact  to  cool  their  drinking  water.  The  water  is  put  into  porous 
jars.  A  little  of  the  water  goes  through  the  jar,  and  by  its  evaporation 
on  the  outside  cools  the  jar  and  the  water  in  it. 

71.  Gases. —  Gases  do  not  have  either  a  definite  shape 
or  a  definite  volume.  The  volume  of  a  gas  depends  upon 
its  temperature  (cf.  §  61)  and  its  pressure  (cf.  §  41). 
Cohesion  between  the  molecules  of  a  gas  is  slight,  because 
the  molecules  are  so  far  apart.  Because  of  the  motion  of 
its  molecules,  a  gas  placed  in  a  vacuum  expands,  until 
it  fills  the  vacuum. 

If  we  force  the  molecules  of  a  gas  closer  together,  we 


68 


HEAT 


TO  BICYCLE 
FIG.  58. 
Bicycle  Pump. 
When     the 
handle   is 
raised,  air  en- 
ters around 
the  piston. 


are  working  against  the  energy  of  the  molecules.  There- 
fore the  compression  of  a  gas  liberates  heat.  This  is 
illustrated  in  the  compression  pumps  (Fig.  58) 
used  to  fill  the  tires  of  bicycles  and  automo- 
biles. They  become  hot. 

Since  compressing  a  gas  heats  it,  expansion 
cools  it.  The  air  rising  from  the  earth  in  con- 
vection currents  (§  67)  is  cooled  as  it  ascends. 
This  is  because  its  volume  increases  as  the 
atmospheric  pressure  becomes  smaller.  The 
heat  needed  to  increase  the  volume  of  the 
rising  air  is  taken  from  the  air  itself.  In  the 
balloon  ascent  described  in  §  41  the  temperature  at  7 
miles  height  was  —60°  F. 

To  change  a  gas  into  a  liquid  we  can  (1)  force  the  molecules  together 
by  increasing  the  pressure;  or  (2)  make  the  motion  of  the  molecules 
smaller  by  lowering  the  temperature  (Fig. 
59);  or  (3)  combine  both  methods. 

The  liquefying  of  air  requires  both  a 
very  low  temperature  and  a  great  pressure. 
The  method  consists,  first,  in  compressing 
the  air  greatly  in  long  tubes;  then  in  re- 
moving the  heat  produced  by  the  com- 
pression; and,  finally,  in  allowing  some  of 
the  compressed  air  to  expand.  The  heat 
needed  to  produce  the  expansion  comes 
from  the  air  that  is  still  under  pressure.  The  removal  of  this  heat 
cools  the  air  until  it  condenses  in  drops  of  liquid. 


S'ulphur  Dioxide 


VSulphur  Dioxide 
FIG.  59. 


Liquefying  Gaseous  Sulphur 
Dioxide  by  Cooling  It. 


72.  Kindling  Temperature. —  All  of  us  know  that 
fires  must  be  "started"  by  some  hot  or  burning  body. 
The  temperature  at  which  a  substance  begins  to  burn  is 
called  its  kindling  temperature.  A  piece  of  iron  picture 


THE  MEASURING  OF  HEAT  69 

cord  will  burn  in  oxygen  (cf.  §  51),  if  tipped  with  burning 
sulphur  to  start  the  action.  A  match  consists  of  several 
substances,  each  of  which  is  used  to  kindle  another  sub- 
stance having  a  higher  kindling  temperature.  Friction 
ignites  the  phosphorus,  the  burning  phosphorus  ignites 
the  sulphur,  and  the  burning  sulphur  sets  the  wood  on 
fire.  A  stick  burns  from  one  end  to  the  other,  each  part 
giving  out  enough  heat  to  ignite  the  part  next  to  it. 

73.  The  Measuring  of  Heat. —  While  the  thermometer 
is  the  instrument  for  finding  the  degree  of  heat  of  a  body, 
the  calorimeter  is  the  instrument  by  means  of  which  we 
get  the  amount  of  heat  in  a  body  (cf.  §  64).  We  measure 
this  amount  by  finding  out  how  much  heat 
the  body  can  give  to  a  certain  weight  of 
water. 

The  simple  calorimeter  is  a  metal  vessel 
(Fig.  60)  with  polished  sides.    A  covering 
of  felt  (a  non-conductor)  prevents  the  air 
from  taking  heat  away  from  the  vessel,  or         FIQ  6Q 
adding  heat  to  it.    Suppose  that  we  wish  to  A  simple 

eter     Surrounded 

find  out  which  holds  more  heat  at  the  same     by  a  Non-con- 

ductor. 

temperature,  lead  or  iron.  We  put  into  the 
calorimeter  a  known  weight  of  water,  at  room  temper- 
ature, let  us  say.  We  then  put  into  the  water  10  g.,  say, 
of  lead  having  a  temperature  of  100°  C.  The  hot  lead 
gives  heat  to  the  water,  until  the  water  and  the  lead  have 
the  same  temperature.  A  thermometer,  kept  in  the 
water,  tells  us  how  many  degrees  the  temperature  of  the 
water  has  been  raised.  We  now  put  into  the  calorimeter 
another  portion  of  water  of  the  same  weight  as  before, 


70 


HEAT 


get  its  temperature,  and  add  10  g.  of  iron  having  a 
temperature  of  100°  C.  In  this  case  the  temperature  of 
the  water  rises  more  than  3  times  as  far  as  when  lead 
was  used.  This  shows  us  that  the  iron  has  more  than  3 
times  as  great  a  heat  capacity,  or  specific  heat,  as  the 
lead.  (See  Appendix,  Table  VII.) 

The  calorimeter  has  very  important,  practical  uses.  A  factory 
using  a  large  amount  of  coal  needs  to  test  different  kinds  of  the  fuel 
(cf.  §  15),  in  order  to  find  which  one  gives  the  most  heat  for  the  least 
money.  The  worker  in  Domestic  Science  wants  to  know  how  much 
heat  the  different  kinds  of  food,  such  as  butter,  potatoes,  beef,  and 
fish,  will  give  out  in  our  bodies  (cf.  §  74).  In  this  way  he  can  get  an 
idea  of  the  values  of  these  foods.  The  heat  that  can  be  obtained  from 
both  the  coal  and  the  food  is  found  by  burning  them  in  a  calorimeter. 
A  calorimeter  such  as  is  needed  to  give  the  heating  value,  in  calories, 
of  a  fuel  or  a  food  (Fig.  61)  is  more  complicated  than 
the  simple  calorimeter,  but  the  principle  according  to 
which  it  " works"  is  the  same.  Some  of  the  fuel  or 
food  is  burned  in  an  inclosed  space  containing  com- 
pressed oxygen,  or  some  oxidizing  substance  (cf.  §  48), 
and  the  heat  given  off  is  imparted  to  a  known  weight 
of  water.  From  the  increase  in  the  temperature 
of  the  water  the  calories  of  heat  given  off  can  be 
calculated. 


FIG.  61. 


74.  Heat  and  Life. —  A  healthy  man  has  a 
temperature  of  98.6°  F.,  or  37°  C.    This  does 

eter.     By  means  ,  -,  .     ,    ,  .      . 

of  it  we  find  the  not  change,  day  or  night,  summer  or  winter, 

amount  of    heat       1    1  ..         .  _       , 

given  off  in  burn-  although  the  temperature  oi  the  air  may 
vary  50°  F.  in  a  day,  and  150°  in  a  season. 
The  body  is  warmed  by  the  changes  (oxidations)  of  its 
own  cells  and  of  digested  food.  We  have  seen  (cf.  §  25) 
that  energy  is  the  capacity  for  doing  work.  The  body  is 


CLOTHING 


71 


FIG.  62. 

Distribution  of  Heat  Obtained 
from  Food. 


thus  a  complex  engine,  using  its  changes  to  produce  heat, 
and  to  enable  it  to  do  work. 

It  has  been  calculated  that  about  3/4  of  all  the  heat  produced  in  the 
body  is  used  to  heat  the  body  (Fig.  62).  A  day's  work  requires  about 
3/ie,  respiration  about  1/6o,  and  the  heart 
about  1/ie.  While  the  oxidation  changes 
are  much  greater  in  some  organs  than 
in  others,  the  heat  is  carried  away  by 
the  blood  as  fast  as  it  is  produced. 
Hence  the  temperature  does  not  vary 
in  any  two  parts  as  much  as  half  a 
degree  Fahr.  The  skin  is,  of  course, 
cooler  than  the  rest  of  the  body,  both 
because  it  is  exposed  to  the  air,  and 
also  because  it  is  cooled  by  the  constant 
evaporation  of  the  perspiration  (cf.  § 
70).  The  excess  heat  of  the  body  acts 
like  the  heat  of  a  stove  in  turning 

perspiration  into  steam.  Ordinarily  the  perspiration  is  evaporated 
as  rapidly  as  it  is  formed,  and  we  do  not  notice  it.  This  is  insensible 
perspiration.  Sensible  perspiring,  or  sweating,  takes  place  only  when 
water  is  given  off  by  the  perspiration  glands  more  rapidly  than  it  can 
be  evaporated  by  body  heat. 

75.  Clothing. —  Man  protects  his  body  against  sudden 
loss  of  heat  by  clothing.  The  best  clothing  for  this  pur- 
pose is  that  which  is  made  of  a  non-conductor  (cf.  §  65), 
and  permits  little  heat  to  escape.  Of  the  common  non- 
conducting materials  the  best  is  wool.  Wool  prevents 
heat  from  coming  to  the  body  as  well  as  its  escape  from 
the  body.  Hence  firemen,  who  are  obliged  to  work  where 
it  is  hot,  use  woolen  clothing  to  keep  cool.  Linen  and 
cotton  are  better  conductors  of  heat  than  wool  is,  and  so 
are  better  for  summer  clothing  than  for  winter  clothing. 


72  HEAT 

But  whether  a  material  will  be  a  conductor  or  a  non- 
conductor depends  largely  upon  whether  it  is  woven  loose- 
ly or  tightly.  For  it  is  the  air  in  the  meshes  of  the  cloth 
that  acts  as  the  best  non-conductor.  Fur  and  feathers 
are  warm  chiefly  because  they  imprison  so  much  air. 
For  the  same  reason  moderately  loose  winter  clothing  is 
warmer  than  tightly  fitting  clothing. 

76.  Sources  of  Heat. —  The  chief  sources  of  heat  are 
the  sun,  body  heat,  the  burning  of  fuels,  friction  and 
collision,  and  electrical  resistance. 

a.  The   Sun. — The  earth   gets   some  heat   from  the 
moon  and  stars  and  its  own  interior,  but  the  amount  is 
small.    Practically  all  the  warmth  of  the  earth's  surface 
and  of  its  atmosphere  comes  from  the  sun.    The  sun  is  so 
far  away,  and  our  earth  is  so  small,  that  we  get  only  a 
very  little  of  the  heat  sent  forth  by  the  sun,—  perhaps 
1  part  out  of  2,000,000,000, —  yet  this  is  enough  to  make 
the  earth  fit  for  living  things  instead  of  a  frozen,  unin- 
habited sphere.    The  gain  and  loss  of  heat  in  the  temperate 
and  frigid  zones  cause  the  seasons  of  these  zones,  and  the 
cutting  off  of  the  sun's  rays  from  any  place  brings  its 
night. 

b.  Fuels. — Man  is  the  only  animal  that  uses  fire.    Other 
animals  and  the  world  of  plants  store  up  some  of  the  energy 
received  from  the  sun,  and  man  uses  them  for  food  and 
fuel.    In  causing  a  fuel  to  unite  with  the  oxygen  of  the 
air,  man  is  getting  back  some  of  the  sun's  energy.    The 
chief  fuels  are  wood,  coal,  charcoal,  coke,  natural  gas, 
petroleum,  and  alcohol.     Petroleum  (cf.   §   121)  is  the 
natural  product  out  of  which  kerosene,  gasoline,  and  par- 


SUMMARY 


73 


affin  (white  wax)  are  prepared.  Coal  is  the  chief  source  of 
illuminating  and  fuel  gas  (cf.  §  124). 

c.  Collision  and  Friction  as  Sources  of  Heat.—  If  you  slap  your 
hands  together  briskly,  they  become  warm.    When  a  bullet  is  stopped 
by  a  rock,  it  becomes  hot.    What  is  the  source  of  the  heat  in  these 
cases?    The  answer  is  that  the  moving  bodies  (the  hands  and  the 
bullet)  have  their  motion  changed  into  heat,  the  motion  of  the  mole- 
cules.   The  heat  is  due  to  the  collision.    When  you  rub  your  hands 
together,  they  become  warm,  because  their  motion  is  partly  changed 
into  heat.    The  loss  of  motion 

is  due  to  the  friction  of  one 
hand  against  the  other. 

Early  man  learned  to  use 
friction  to  kindle  his  fires  (Fig. 
63),  and  thus  exchanged  mus- 
cular energy  for  heat.  Later 
he  obtained  sparks  by  striking 
together  flint  and  steel,  or 
flint  and  iron  pyrites  ("pi-rl'- 
tes";  also  caUed  "  fools'  gold," 
from  its  deceptive  color).  In 
the  modern  match  man  is  still 
exchanging  motion  for  heat; 
for  he  uses  friction  to  kindle 
the  match. 

d.  Electrical  Resistance. — 
The    energy    of    the    electric 

current  is  easily  changed  into  heat,  and  gives  us  electric  lights, 
heaters,  and  furnaces.  We  can  understand  these  better  after  we  have 
studied  Chapter  VIII. 


FIG.  63. 

Batua  Fire-Drilling,  Congo  Free  State.     Copy- 
right, 1912;  Frederick  Starr. 


77.  Summary. — Bodies  usually  expand  when  heated,  and  con- 
tract when  cooled.  This  is  explained  by  the  theory  that  matter  is 
composed  of  molecules,  and  that  heating  separates  them  further,  while 
cooling  causes  them  to  come  closer  together. 


74  HEAT 

Thermometers  measure  differences  of  expansion  between  mercury 
and  glass. 

The  "freezing  point"  of  a  thermometer  is  the  temperature  of 
melting  ice.     The  "  boiling  point "  mark  is  the  temperature  of  steam 
given  off  by  water  that  is  boiling  under  standard  pressure. 
.  =  (Cent.X9A)+32. 
=  5/9(Fahr.-32). 

Degree  of  heat  is  temperature.  It  depends  upon  the  rapidity  of 
molecular  motion. 

Quantity  of  heat  in  a  body  depends  upon  the  temperature  and  the 
mass;  also  upon  heat  capacity  (cf.  §  73). 

The  calorie  is  the  unit  of  heat  quantity. 

Heat  is  distributed  by  conduction  (or  contact),  by  radiation,  and  by 
convection. 

Convection  currents  are  set  up  in  liquids  or  gases  if  they  are  heated 
from  the  bottom  or  cooled  from  the  top. 

The  three  physical  forms  of  matter  are  solids,  liquids,  and  gases. 
They  depend  on  the  cohesion  and  the  energy  of  the  molecules. 

Heat  of  melting,  or  of  fusion,  is  the  number  of  calories  of  heat 
needed  to  melt  1  g.  of  a  solid. 

Heat  of  freezing  is  the  number  of  calories  given  off  in  the  freezing 
of  1  g.  of  a  liquid.  It  is  equal  to  the  heat  of  melting. 

Water  expands  when  it  freezes;  most  liquids  contract. 

Heat  taken  up  in  the  change  of  liquid  to  vapor  is  given  off  in  the 
condensation  of  the  vapor. 

Compression  of  a  gas  liberates  heat.  Expanding  gases  take  up 
heat;  that  is,  become  cold. 

Kindling  temperature  is  the  temperature  at  which  a  substance 
begins  to  burn. 

A  calorimeter  is  an  apparatus  in  which  the  heat  given  off  in  burn- 
ing, or  in  some  other  change,  can  be  given  to  some  water,  and  so 
measured. 

The  human  body  is  a  complex  engine.  It  uses  the  changes  in  its 
cells  and  in  food  to  produce  heat  and  the  ability  to  do  work. 

Evaporation  of  perspiration  keeps  the  body's  temperature  constant. 

Wool  makes  the  best  clothing  for  those  exposed  to  extremes  of 
temperature. 


EXERCISES  75 

Sources  of  heat  are  the  sun,  fuels,  collision,  friction,  and  electrical 
resistance. 

78.  Exercises. 

1.  If  you  mix  100  g.  of  water  at  80°  C.  with  100  g.  of  water  at  0°  C., 
what  temperature  will  the  mixture  have? 

2.  How  many  calories  are  needed  to  melt  100  g.  of  ice?    If  you  mix 
100  g.  of  water  at  80°  C.  with  100  g.  of  ice  at  0°  C.,  what  will  happen? 
What  will  the  temperature  of  the  mixture  be? 

3.  If  a  glass  fruit  jar  is  filled  completely  with  water,  then  sealed, 
and  put  outdoors  in  zero  weather,  what  is  likely  to  happen?    Why? 

4.  If  you  open  the  valve  of  a  full  bicycle  tire,  the  escaping  air  feels 
cold;  why? 

5.  If  steam  at  100°  C.  enters  the  steam  coil  of  a  room,  and  water  at 
100°  C.  leaves  the  coil,  how  is  the  roorn  heated? 

6.  Why  does  sprinkling  a  lawn  in  hot  weather  cool  the  air? 

7.  If  some  liquid  air  is  poured  into  an  open  beaker,  its  temperature 
does  not  rise  above  — 182.5°  C.,  no  matter  how  warm  the  room  is. 
Explain. 

8.  What  do  we  mean  by  saying  that  the  specific  heat  of  water  is  9 
times  that  of  iron? 

9.  Why  does  a  nail  struck  repeatedly  with  a  hammer  become  hot? 
Why  does  a  bit  used  to  drill  holes  in  a  board  become  hot?    What 
causes  a  "hot  box"  on  a  railway  car?    Give  other  illustrations  of  the 
same  phenomenon. 


CHAPTER  V 

WATER 

79.  How  Water  Occurs  in  Nature. —  We  commonly 
think  of  water  as  a  clear,  easily  poured  liquid;  we  must 
also  think  of  it  as  a  solid :  snow,  frost,  and  ice,  and  as  a 
gas  or  vapor :  steam.  Water  is  very  abundant,  not  only 
in  rivers,  lakes,  and  the  ocean,  but  also  in  the  earth's 
solid  crust.  No  matter  where  we  dig,  we  find  it — even  in 
the  desert.  The  atmosphere  likewise  contains  a  great 
deal :  as  steam.  Water  makes  up  a  large  part  of  all  plants 
and  animals.  The  following  table  shows  how  much  of 
our  bodies  and  our  food  is  water: 

Human  body.  ....   70%        Watermelon.  .'.  .  .  .   92% 

Milk 87%        White  bread 35% 

Potatoes 78%        Beef 62% 

Natural  water  is  never  pure.  The  rain  gathers  material 
from  the  atmosphere  (cf.  §  58) ;  the  water  that  flows  over 
or  through  the  earth's  crust  dissolves  substances  from 
the*  soil  and  the  rock;  and  both  rain  and  running  water 
take  up  living  creatures,  such  as  bacteria  (cf.  §§56  and 
324).  Rivers  and  lakes  become  impure  because  of  the 
sewage,  or  waste  matter,  of  the  cities,  factories,  and  farms 
upon  their  banks. 

The  purest  natural  water  is  probably  obtained  by  melt- 
ing some  ice  obtained  from  a  pure  source. 

76 


DRINKING   WATER 


77 


80.  Substances  Dissolved  in  Natural  Water. —  Lakes 
and  rivers  are  usually  fresh  because  the  salty  substances 
brought  into  them  are  also  carried  away;  but  the  ocean 
becomes  more  and  more  loaded  with  dissolved  material. 
The  same  is  true  of  such  lakes  as  Great  Salt  Lake  and  the 
Dead  Sea.  The  reason  is  that  while  these  bodies  receive 
both  water  and  dissolved  substances,  only  the  water 
evaporates.  The  solids  are  left  behind.  Nearly  2.7  per 
cent  of  sea  water  is  common  salt. 

Mineral  waters  contain  so  much  solid  material  in  solution  that  it  is 
usually  perceptible  to  the  taste.  The  most  common  substances  in 
mineral  waters  are  salt,  soda,  potash,  limestone,  gypsum,  and  com- 
pounds of  iron  and  of  sulphur.  As  many  as  15  grams  of  solids  are 
sometimes  present  in  one  liter  of  mineral  water.  Salt  springs  and 
wells  furnish  most  of  our  table  salt  (cf.  §  108  and  Fig.  84). 

COMPOSITION  OF  SOME  NATURAL  WATERS 


Source  of  Water 

Grams  of  Solids  in 
10GO  g.  of  Water 

Cubic  Centimeters  of  Gases 
in  1  1.  of  Water 

Nitrogen 

Oxygen 

Carbon 
Dioxide 

Rain 

.029 
.097 
.282 
.438 
35.25 
40.00 
228.60 
271.40 

13.1 
15.0 
15.8 

12.Q 

6.4 

7.4 
8.5 

6.'0 

1.3 
30.0 
1.1 

i7'6 

Rivers  and  Lakes  
Springs  

Deep  Wells  
English  Channel  
Mediterranean  Sea.  .  .  . 
Dead  Sea  

Lake  Elton 

81.  Drinking  Water. —  By  "pure  water"  different 
classes  of  people  mean  different  things,  for  each  is  thinking 
of  some  impurity  that  is  especially  objectionable  to  him. 
If  the  water  is  to  be  used  for  drinking,  the  chief  impurities 


78 


WATER 


we  are  troubled  about  are  injurious  bacteria,  and  the  de- 
caying matter  upon  which  they  live.  Dissolved  gases  and 
minerals  are  not  usually  considered  impurities  in  a  drink- 
ing water;  but  if  the  bacteria  of  certain  diseases,  such  as 
typhoid  fever,  get  into  the  water,  we  may  " catch'7  the 
disease  by  taking  the  bacteria  into  the  stomach.  Hence 
drinking  water  should  be  tested  carefully.  This  is  espe- 
cially true  if  the  source  of  the  water  is  not  well  known,  or 
if  it  is  suspicious.  Whether  a  water  is  pure  or  impure 
cannot  be  told  by  its  appearance:  a  dirty  looking  water 
may  be  safe  to  drink,  while  one  clear  as  crystal  may  be 

filled  with  deadly 
germs.  Shallow 
wells  are  always  sus- 
picious ;  for  filth  may 
be  washed  in  from 
the  surface  by  the 
rain,  and  kitchen 
drains,  outbuildings, 
or  barns  may  be 
sufficiently  near  to 
pollute  the  well  (Fig. 
64).  We  must  re- 
member that  ice 
made  from  polluted 
water  is  also  dan- 
gerous. The  disease  germs  are  not  killed  by  freezing,  but 
live  on  in  an  inactive  state.  They  become  active  again 
when  they  find  lodging  in  our  bodies,  or  in  favorable 
food,  such  as  milk. 


FIG.  64. 

A  well  may  be  polluted  by  a  cesspool  or  by  drainage 
from  a  barn. 


PURIFYING  WATER  79 

82.  Hardness  of  Water. —  To  the  manufacturer ' '  pure  " 
water  usually  means  water  that  can  be  used  in  boilers, 
to  produce  steam.    The  most  objectionable  impurity  from 
his  point  of  view  is  the  "hardness"  of  the  water.    Hard- 
ness is  also  harmful  in  water  to  be  used  in  the  house- 
hold for  bathing  and  for  the  washing  of  clothes.    Water 
is  said  to  be  "hard"  if  it  does  not  wet  the  skin  readily, 
and  if  soap  put  into  the  water  forms,  at  first,  an  in- 
soluble scum.     Suds,  or  lather,  is  not  formed  in  hard 
water  until  the  hardness  is  removed  by  the  soap;  hence 
hardness  is  defined  as  the  soap-consuming  power  of  a 
water.    Distilled  water,  water  from  melting  ice,  and  rain 
water  form  a  lather  almost  immediately;  hence  they  are 
called  "  soft  "  waters.    Some  of  the  impurities  that  cause 
hardness  become  insoluble,  and  settle,  when  the  water  is 
boiled.    In  this  case  the  hardness  is  said  to  be  temporary. 
Hardness  that  cannot  be  removed  by 

boiling  is  called  permanent  hardness 
(c/.§226). 

If  a  boiler  is  filled  repeatedly  with  hard 
water,  it  becomes  clogged  with  a  deposit  — 
"boiler  scale" — just  as  a  kettle  does  (Fig.  65). 
Iron  is  a  conductor  of  heat  (cf.  §  65) ;  hence  the 

walls  of  a  new  iron  boiler  cannot  become  much  The  kettle  is  lined  with  solids 
hotter  than  the  water  in  the  boiler.   But  boiler        deposited  from  boiling 
scale  is  so  poor  a  conductor  that  a  boiler  con- 
taining much  of  it  needs  to  be  heated  very  hot,  or  the  water  will  not 
boil.     As  a  result  of  this  over-heating,  the  "scale"  is  often  broken  up 
into  substances  that  act  upon  the  iron,  and  weaken  it.    Boiler  scale 
has  caused  very  serious  explosions  and  loss  of  life. 

83.  Purifying  Water. —  Water  may  be  purified  — 

(1)  by  distilling  it ;  (2)  by  boiling  it ;  (3)  by  filtering  it. 


80 


WATER 


Overflow 


Distillation  consists  in  heating  a  liquid  until  it  bpils, 
and  then  passing  the  vapor  through  a  condensing  appara- 
tus to  convert  it  back  into  the  liquid  state.  The  solid 

substances,  such 
as  salt,  limestone, 
gypsum,  etc.,  do 
not  boil  off,  but 
remain  behind  in 
the  boiler.  The 
form  of  distilling 
apparatus  much 
used  in  laborato- 
ries is  shown  in 
Fig.  66. 

Fia.  66. 
Distillation  of  Water;  Liebig's  Condenser.  The     Condenser    is 

known    as    Liebig's 

condenser,  after  the  celebrated  scientist  of  that  name.     It  is  of  glass, 
and  consists  of  an  inner  tube  for  condensing  the  vapor,  and  an  outer 
jacket  for  the  cooling  liquid,  which 
is  usually  water.    For  distillation 
on  a  larger  scale  a  boiler  and 
a   "worm"  condenser  are  used 
(Fig.  67). 

Other  liquids  may  be  distilled 
like  water.  Thus,  while  water 
boils  at  100°  C.,  alcohol  boils  at 
79°  C.  If  a  mixture  of  alcohol  and 
water  is  distilled,  the  alcohol  boils  FIG.  67. 

Off  first,  and  the  tWO  may  thus  be  Large  Still  and  Worm  Condenser. 


Boiling  removes  the  temporary  hardness  of  water,  and  kills  the 
germs.  Since  the  taste  of  natural  water  is  due  to  the  dissolved  gases 
and  solids  it  contains,  distilled  water  tastes  very  "flat."  Boiled 


FILTERING 


81 


placed  in  the  funnel, 
liquid  is  poured  from  a 
beaker,  down  a  glass  rod, 
upon  the  filter.  The  filtrate 
runs  through  the  filter. 


water  is  more  agreeable,  because  some  dissolved  solids  are  still  present; 
but  both  kinds  of  water  are  better  if  they  are  aerated;  that  is,  if  they 
are  made  to  dissolve  air.     We  can  add  the  air 
to  a  water  by  filtering  the  water  through 
porous  stone,  or  by  pouring  the  water  several 
times  from  one  vessel  to  another. 


84.  Filtering.  —  A  filter  is  a  screen 
or  sieve  with  openings  so  small  that 
only  liquids  and  the  substances  dis- 
solved in  them  can  get  through. 
Substances  suspended  in  the  Jiquid, 
which  make  the  liquid  roily,  or  turbid, 
can  not  get  through.  In  the  laboratory 
we  make  a  filter  by  folding  a  piece  of 
porous  paper,  as  shown  in  Fig.  68,  and 
placing  it  in  a  funnel.  If  a  milky  mixture  of  water  and 
powdered  chalk  be  poured  upon  the  filter,  the  water 

goes  through,  but  the  chalk  does 
not. 

In  household  filters  (Fig.  69)  por- 
ous stone  and  charcoal  are  used  as 
filtering  materials.  These  strain 
out  the  suspended  impurities  of 
the  water,  including  the  bacteria. 
However,  unless  a  filter  is  cared 
for,  it  may  become  so  clogged  with 
organic  matter  that  it  will  serve  as 
a  breeding-place  for  bacteria,  in- 
stead of  removing  them.  Water  filters  should  be  cleaned 
frequently,  and  exposed  to  direct  sunlight,  to  keep  them 
fresh  and  wholesome.  This  is  especially  true  of  filters 


Charcoel 


FlG.  69. 
A  Household  Filter. 


82 


WATER 


attached  to  faucets,  because  of  the  large  volume  of  water 
that  passes  through  them  daily. 

85.  Filtering  City  Water.— The  best  natural  filter  is 
clean  sand.  It  is  loose,  and  contains  much  air;  hence 
oxidizing  bacteria  can  penetrate  far  into  it.  If  the  sand 
is  not  kept  soaked  too  long  at  a  time,  impure  water  that 

passes  through  it  will  be 
made  fit  for  drinking. 
A  soil  containing  much 
clay  does  not  make  a 
good  filter,  because  clay 
is  too  compact. 

In  filtering  water  for  cities 
(Fig.  70)  men  run  the  water 
of  rivers  or  lakes  through 
beds  of  sand.  After  soaking 
through  the  sand  the  water 
enters  reservoirs,  from  which 
it  is  distributed  through  the 
water  "mains"  of  the  city. 
But  the  large  filters,  like  the 
small  ones,  need  to  be  emptied 

often,  and  allowed  to  lie  idle,  so  that  the  sand  may  be  purified  by 

the  direct  action  of  sunlight  and  air. 

Coagulation  Filters.— In  some  cases  a  coagulating,  or  clotting, 
substance,  such  as  alum,  is  added  to  the  water  before  it  enters  the  sand 
filters.  The  alum  causes  the  clay  particles,  which  of  themselves  settle 
only  very  slowly,  to  flock  together  and  to  come  down  rapidly,  carrying 
decaying  matter  and  germs  with  them.  Coke  dust  is  often  mixed 
with  the  sand  to  improve  the  quality  of  the  filter. 


FIG.  70. 
Filter  Beds  of  a  City  System;  Evanston,  111. 


WHY  ICE  FORMS  ONLY  AT   THE  SURFACE  83 

86.  Exercises. 

1.  Hard  cookies  placed  in  a  box  containing  fresh  bread  become  soft 
and  mellow;  why?     Why  do  crackers  lose  their  crispness  when  taken 
out  of  their  box? 

2.  Tell  why  a  potato  loses  weight  when  baked. 

3.  Why  does  candy  become  sticky,  and  why  does  salt  "cake,"  in 
damp  weather? 

4.  The  Jordan  River  flows  into  Lake  Utah,  and  Lake  Utah  empties 
into  Great  Salt  Lake.    Would  you  expect  Lake  Utah  to  have  fresh 
water  or  salty?    Why? 

5.  Tell  how  the  crew  of  a  ship  can  prepare  fresh  water  out  of  sea 
water?    How  does  nature  do  it? 

6.  Name  some  of  the  ways  in  which  dirty  water  thrown  into  the 
yard  is  purified  by  nature.    Why  should  such  water  never  be  thrown 
near  a  well  or  cistern? 

7.  Why  does  moisture  condense  on  the  windows  of  the  house  on  a 
cold  wash  day? 

8.  Why  should  bottles  of  alcohol,  gasoline,  and  turpentine  be  stop- 
pered? 

87.  Why  Ice  Forms  Only  at  the  Surface. —  Since  ice 
is  lighter  than  water  (cf.  §  70),  it  floats,  and  the  ice  cover- 
ing usually  prevents  the  water  beneath  from  freezing.  But 
the  chief  reason  why  lakes  and  streams  do  not  freeze  to 
a  great  depth  is  that  water  is  most  dense,  or  heavy  (cf. 
§  33),  not  at  0°  C.,  the  freezing  temperature,  but  at  4°  C. 
Let  us  see  the  results  of  this  fact :  — 

A  lake  or  stream  is  cooled  chiefly  from  the  top,  where  it 
touches  the  cold  air.  Now,  when  a  lake  having  water  at, 
let  us  say,  10°  C.,  is  cooled  by  air  at  0°  C.,  or  below,  the 
surface  layer  becomes  colder  than  10°  C.,  and  heavier, 
and  so  sinks  to  the  bottom,  while  a  warmer  layer  takes  its 
place.  This  movement  of  water  goes  on  until  all  the 
water  is  cooled  to  4°  C.  But  as  the  upper  layer  of  water, 


84 


WATER 


which  is  now  at  4°  C.,  is  cooled  further,  it  becomes  lighter 
than  the  water  at  4°  C.,  and  floats  upon  the  warmer  water. 
When,  finally,  the  surface  of  the  water  freezes,  the  ice 
that  is  formed  also  floats.  Hence  the  water  below  the 
ice  is  rarely  cooled  below  4°  C.  Because  of  this  fact  water 
animals  and  plants  survive  the  winter,  and  live  even  in 
Arctic  waters. 

88.  Artificial  Ice. —  The  supply  of  natural  ice  is  so  un- 
certain, especially  in  warm  climates,  that  men  have  been 


Hot  Gas   130°C 


17°C 


-15°C 


Co.mpreseion   Pump 


Expansion  Coils  and    Ice    Molds 


FIG.  71. 

Cooling  Brine  for  Ice  Making  by  the  Expansion  of 
Compressed  Liquid  Ammonia. 


forced  to  make  ice  by  artificial  freezing.  To  freeze  the 
water  some  liquid  is  used  that  boils  at  a  low  temperature. 
Usually  the  liquid  is  liquid  ammonia.  This  is  not  "am- 
monia water,"  but  the  gas,  ammonia,  which  has  been 
liquefied  by  pressure.  The  liquid  ammonia  is  made  to 
evaporate  rapidly  by  the  removal  of  the  pressure.  The 
turning  of  the  liquid  into  the  gas  requires  heat,  just  as 


STEAM  85 

the  turning  of  water  into  steam  does.    In  the  ammonia  ice 
apparatus  the  heat  comes  from  the  water  to  be  frozen. 

The  apparatus  is  shown  in  Fig.  71.  In  this  apparatus  the  water 
is  not  frozen  directly  by  the  evaporation  of  the  liquid  ammonia;  but  a 
brine  is  cooled  to  — 15°  C.  or  — 20°  C.,  and  this  cold  liquid  is  used  to 
freeze  the  water.  The  brine  is  a  water  solution  of  salt  or  of  calcium 
chloride,  and  freezes  far  below  the  freezing  temperature  of  water. 
The  cold  brine  is  also  used  in  cold-storage  warehouses,  and  in  refriger- 
ator cars,  to  produce  a  low  temperature.  In  this  way  butter,  eggs, 
meat,  fruit,  etc.,  are  kept  cold,  and  prevented  from  spoiling  (Fig.  72). 


FIG.  72.     . 

Rooms  for  storage  of  meat  are  cooled  by  means  of  a  cold  brine 
distributed  through  pipes. 

"Iceless"  refrigerators  are  now  being  made.  They  are  really  refriger- 
ating machines,  and  are  kept  cold  by  the  rapid  evaporation  of 
liquid  ammonia. 

89.  Steam. —  Steam  is  water  in  the  vapor  form.    When 
steam  issues  briskly  from  a  vessel  of  boiling  water,  as 


86  WATER 

from  the  spout  of  a  tea-kettle,  it  is  invisible  until  it  con- 
denses to  fine  drops,  some  distance  away.  The  fine  drops 
are  liquid  water,  not  steam.  Clouds  are  made  of  similar 
droplets :  ' ' fog,"  not  of  steam. 

While  water  freezes  at  a  definite  temperature  (0°  C.  or 
32°  F.),  it  is  changed  into  steam  at  any  temperature. 
Even  ice  and  snow  pass  directly  into  steam  (evaporate) 
on  a  cold  winter's  day,  without  melting. 

Like  air  and  other  gases,  steam  has  pressure.  At  the 
ordinary  temperature  the  pressure  of  the  steam  given  off 
by  water  is  small  (cf.  Appendix,  Table  VIII) ;  but  as  the 
temperature  of  the  water  rises,  its  steam  has  a  greater  and 
greater  pressure,  until  at  100°  C.,  or  212°  F.,  the  steam  has 
the  same  pressure  as  the  air  (760  mm.).  The  steam  then 
sweeps  the  air  completely  out  of  the  vessel  in  which  the 
water  is  being  heated.  We  say  that  the  water  is  boiling, 
and  we  call  100°  C.,  or  212°  F.,  the  boiling  point  of  water 
(cf.  §  62). 

90.  The  Boiling  Point  Changes  with  Pressure. —  If 

water  is  boiled  in  a  closed  vessel,  more  and  more  steam  is 
packed  into  the  space  above  the  liquid  water,  and  the 
pressure  of  the  steam  increases  accordingly.  Under  the 
increased  pressure  of  the  steam,  the  water  now  boils 
above  100°  C.  When  the  steam  has  twice  the  atmos- 
pheric pressure  (2X760  mm.),  water  boils  at  121°  C.  In  a 
locomotive  boiler  producing  steam  at  13  "  atmospheres " 
pressure  (191  pounds  to  the  square  inch)  water  boils  at 
192°  C.,  or  378°  F.  When  steam  at  high  pressure  is  allowed 
to  escape,  it  expands  greatly.  This  is  the  source  of 
motion  in  a  steam  engine  (cf.  §  24). 


SOLUTIONS 


87 


Condenser 


When  the  pressure  under  which  water  boils  is  less  than  760  mm., 
the  boiling  point  is  less  than  100°  C.  (cf.  Appendix,  Table  VIII). 
Sugar  refiners  make  use  of  this  fact  in  boiling  off  the  water  from  dilute 
syrup.  If  the  water  were  removed  at  the  ordinary  pressure,  the  syrup 
would  boil  so  high  that  the  sugar  would  be  spoiled.  By  the  use  of 
evaporating  vessels  called  "vacuum  pans,"  which  are  covered  with 
tight  hoods  (Fig.  73), 
this  is  avoided.  If 
the  air  is  removed 
from  the  pans  until 
its  pressure  is  only 
233  mm.,  the  water 
boils  off  at  70°  C. 
without  injuring  the 
sugar.  Salt  is  ob- 
tained from  salt  brines 
in  the  same  way. 

The  boiling  point 
of  water  falls  about 
1°C.  for  every  960 
feet  we  ascend  above 
sea  level.  Thus,  at 
the  city  of  Mexico, 

7,500  ft.  above  the  sea,  water  boils  at  92.3°  C.,  while  at  Denver,  5,000 
ft.  high,  it  boils  at  about  95°  C. 

91.  Solutions. —  If  we  put  salt  or  sugar  into  water,  the 
solids  disappear.  We  say  they  dissolve  in  the  water.  They 
have  not  really  disappeared,  however,  for  they  give  their 
taste  and  other  properties  to  the  water.  We  call  the 
water  the  solvent,  and  the  dissolved  substance  the  solute. 
The  mixture  of  solute  and  solvent  is  called  a  solution. 
Solutions  in  which  alcohol  is  the  solvent  are  called  tinc- 
tures. If  the  solute  is  of  some  other  color  than  white, 
its  water  solution  will  usually  be  colored.  A  minute 


FIG.  73. 

Vacuum  Pan.    Water  is  being  distilled  at 
"reduced  pressure." 


88  WATER      . 

amount  of  potassium  permanganate,  or  of  aniline  violet, 
shows  a  remarkable  power  of  coloring  water.  But 
whether  colorless  or  colored,  true  solutions  are  clear,  not 
roily  (cf.  §  84). 

Milk  is  a  mixture  of  water,  sugar,  etc.,  with  suspended  particles  of 
fat.  The  fat  is  very  finely  divided,  and  the  casein  of  the  milk  (cf. 
§  357)  prevents  the  water  and  fat  from  separating  at  once  into  two 
distinct  layers.  After  a  while,  however,  the  fat  (cream)  rises  to  the 
top.  Such  a  mixture  is  called  an  emulsion. 

92.  Properties  of  Solutions. —  A  solute  not  only  im- 
parts its  taste  and  color  to  a  solution,  but  it  makes  the 
boiling  point,  freezing  point,  and  density  of  the  solution 
differ  from  those  of  the  solvent.     A  solution  of  a  solid 
boils  at  a  higher  temperature,  and  freezes  at  a  lower 
temperature,  than  the  pure  solvent.     Thus,  a  solution  of 
40  g.  of  salt  in  100  g.  of  water  boils  at  about  108°  C.     A 
saturated  salt  brine  does  not  freeze  until  the  temperature 
is  about  —22°  C.     Because  of  its  dissolved  solids,  ocean 
water  rarely  freezes  in  temperate  latitudes. 

When  a  dilute  salt  brine  freezes  partly,  but  not  wholly, 
most  of  the  salt  remains  in  the  solution,  and  the  ice  is 
nearly  fresh. 

A  solution  of  a  solid  has  a  greater  density  than  the 
solvent.  Thus,  while  a  liter  of  pure  water  weighs  about 
1000  g.,  the  same  volume  of  sea  water  weighs  about  1026 
g.  (qf.  §  80). 

93.  Freezing  Mixtures. —  When  most  solids   dissolve 
in  water,  they  lower  the  temperature  of  the  water.     Thus, 
if  equal  parts,  by  weight,  of  ammonium  nitrate  and  water 
are  mixed  at  0°  C.,  the  temperature  falls  to  —15°  C. 


CRYSTALS 


89 


We  have  learned  (c/.  §  69)  that  when  ice  is  placed  in  water,  the  heat 
needed  to  melt  the  ice  (80  calories  for  each  gram)  comes  from  the 
water;  hence  the  water  is  cooled  to  its  freezing  point,  0°  C.  Now,  when 
ice  is  mixed  with  salt,  the  salt  dissolves  in  the  water  formed  by  the 
melting  of  the  ice.  We  thus  get  a  salt  brine.  The  heat  needed  to 
melt  the  ice  comes  from  the  brine,  and  cools  it  to  its  freezing  point, 
—  22°  C.  If  cream  or  ' '  ices  "  are  placed  in  this  brine,  heat  is  taken  out 
of  them  until  they  are  frozen. 

94.  Solubility. —  By  the  solubility  of  a  solid  we  mean 
the  weight  of  it  that  will  dissolve  in  a  definite  amount, 
say,  100  grams,  of  the  solvent.  We  know  that  if  we  add 
too  much  sugar  to  our  tea  or  coffee,  some  of  it  will  not 
dissolve,  even  though  we  stir  the  liquid  vigorously.  The 
tea  or  coffee  is  then  said  to  be  "  saturated  "  with  sugar. 
If  a  liquid  is  hot,  it  can  usually  dissolve  more  solid  than 
when  cold. 

A  solid  that  is  soluble  in  water  may  be  insoluble  in 
another  solvent.  Thus,  salt  does  not  dissolve  in  alcohol. 
Camphor  and  shellac  dissolve  in  alcohol,  but  not  in  water. 

The  accompanying  table  shows  that  substances  differ  greatly  in 
solubility,  and  also  that  the  solubility  of  solids  generally  increases  as 
the  temperature  rises. 


Substance 

Grams  Soluble  in  100  g.  Water  at 

o°c. 

20° 

50° 

70° 

100° 

Potassium  nitrate  (saltpeter)  
Sodium  chloride  (salt) 

13 
35 
3 
15 
6 

32 
36 

7 
22 
13 

85 
37 
20 

32 

140 
38 
32 

iis 

246 
39 
59 
73 

Potassium  chlorate 

Copper  sulphate  (blue  vitriol) 

Alum  

95.  Crystals. —  The  table  of  solubility  shows  us  that 
water  at  100°  C.  can  dissolve  more  of  the  substances 


90 


WATER 


FIG.  74. 

Crystals  of  Salt  (A),  Alum  (B),  and  Blue 
Vitriol  (C7). 


named  than  water  at  20°  C.  (the  ordinary  temperature). 
Suppose  we  were  to  saturate  some  water  at  100°  C.  with 
common  salt,  and  were  then  to  let  the  solution  cool  to 
20°;  what  might  we  expect  to  happen?  We  might  expect 
part  of  the  salt  to  be  deposited  as  a  solid.  If  we  examined 

the  deposited  salt, 
we  would  find 
that  it  consisted 
of  small  cubes 
(Fig.  74,  A).  We 
would  also  get 
cubes  of  salt  if 
we  were  to  let  some  salt  solution  evaporate  slowly  at  the 
ordinary  temperature.  The  cubes  are  crystals  of  salt. 

If  we  make  a  hot,  saturated  solution  of  alum,  and  let 
it  cool  slowly,  we  shall  get  crystals  like  Fig.  74,  B;  while 
crystals  of  blue  vitriol  are  like  I  ig.  74,  C.  All  of  these 
crystals  have  flat  (plane)  faces  and  straight  edges  arranged 
in  a  definite  way. 

Each  substance  has  its  own  crystalline  form,  but  the  crystals  may  be 
imperfect  if  they  are  deposited  on  the  sides  of  the  vessel.    The  more 
slowly   the   crystals   separate 
from  solution,  the  larger  they 
will   be.      Sugar    crystallized 
upon  a  string  which  is  sus- 
pended in  the  sugar  solution 
is  called  "rock  candy"  (Fig. 


FIG.  75. 

Crystals  of  Sugar  (A),  Quartz  (B),  and 


75,  A).     Sulphur  crystallizes 

(Fig.  3)  from  a  liquid  called  Diamond  (co 

carbon  disulphide. 

Crystals  may  be  formed  not»only  from  solution,  but  also  by  the 
freezing  of  a  liquid;  as  ice  is  made  by  the  freezing  of  water.    Ice  is 


SUMMARY  91 

composed  of  small  crystals  packed  closely  together.    The  separate 
crystals  can  be  seen  when  freezing  begins,  and  in  the  form  of  snow  and 


Fio.  76. 
Crystals  of  Snow. 


frost.      Snowflakes  take  on  many  forms  (Fig.  76),  but  all  are  six-sided 
or  six-pointed. 

Substances  that  do  not  crystallize  are  said  to  be  amorphous,  that 
is,  "without  form."  Glass  and  many  gums  are  examples. 

96.  Summary.— Water  exists  as  solid,  liquid,  and  vapor.  It  is 
very  abundant  in  nature,  but  natural  water  is  rarely  pure. 

Mineral  waters  contain  so  much  material  that  it  can  be  tasted. 
The  sea  contains  even  more  dissolved  material  than  mineral  waters. 

Drinking  water  is  considered  pure  if  it  does  not  contain  too  much 
mineral  matter,  and  if  it  is  free  from  injurious  "germs." 

Hardness  of  water  is  its  soap-consuming  power.  It  may  be  tem- 
porary or  permanent. 

Boiler  scale  is  a  deposit  left  in  steam  boilers  and  kettles  that  use 
hard  water. 

Water  is  purified  by  distillation,  boiling,  filtration,  and  ' 'softening/' 

Distillation  is  changing  a  liquid  into  its  vapor,  and  then  condensing 
the  vapor.  The  impurities  are  left  behind. 

The  "flat"  taste  of  distilled  and  boiled  water  is  due  to  the  absence 
of  dissolved  substances,  including  air. 

Filters  "strain  out"  the  suspended  impurities  of  water  and  give  a 
large  surface  for  the  oxidizing  bacteria  of  the  air. 

Water  freezes  at  0°  C.  (32°  F.).  It  expands  as  it  freezes;  hence  ice 
floats. 

Artificial  ice  is  made  by  the  use  of  the  principle  that  evaporation 
requires  heat.  The  heat  needed  to  vaporize  liquid  ammonia  is  taken 
from  the  water  to  be  frozen. 


92  WATER 

Steam  is  the  gaseous  form  of  water.  Water  and  ice  change  to  steam 
at  all  temperatures.  At  100°  C.  the  steam  from  boiling  water  has  a 
pressure  equal  to  the  pressure  of  the  atmosphere. 

A  solution  consists  of  solvent  and  solute.  An  emulsion  is  a  mixture 
in  which  the  suspended  substance  is  so  finely  divided  that  it  separates 
itself  from  the  solvent  very  slowly. 

Solubility  of  a  solid  is  the  weight  of  it  that  will  dissolve  in  a  definite 
weight,  usually  100  g.,  of  water  or  other  solvent. 

Crystals  are  solid  bodies  that  take  regular  shapes  when  they  sep- 
arate from  solution  or  from  the  liquid  state.  Non-crystalline  sub- 
stances are  amorphous. 

97.  Exercises. 

1.  If  water  were  most  dense  at  0°  C.,  what  effect  would  this  fact 
have  upon  the  depth  of  ice  in  winter? 

2.  If  a  test  tube  of  water  is  placed  in  a  cup  of  ether,  and  a  rapid 
current  of  air  is  forced  through  the  ether,  the  water  may  be  frozen. 
Why? 

3.  Which  should  be  kept  in  the  colder  room  of  a  storage  warehouse, 
eggs  or  meat? 

4.  The  sharp  edges  of  a  piece  fo  ice  become  rounded  off  even  in 
very  cold  weather;  why? 

5.  In  making  " fudges,"  or  the  filling  of  French  candies,  why  is  the 
candy  first  cooled  without  being  disturbed,  and  afterwards  stirred 
rapidly? 

6.  Can  you  dissolve  salt  in  water,  and  then  recover  the  salt  un- 
changed by  boiling  off  the  water?    Can  you  do  the  same  with  sugar? 
Why? 

7.  At  Quito,  in  Ecuador,  water  boils  at  90°  C.,  too  low  for  the  cook- 
ing of  potatoes;  why?    Can  you  suggest  how  you  could  make  water 
boil  at  100°  C.  in  Quito? 

8.  How  is  salt  commonly  obtained  from  salt  water?    In  Northern 
Russia  the  salt  makers  remove  much  of  the  water  by  partly  freezing 
the  salt  solution,  and  so  save  fuel.    How  is  this  possible? 


EXERCISES  93 

9.  Why  is  it  easier  to  swim  in  the  ocean  than  in  fresh  water? 

10.  If  sugar  is  dissolved  in  a  cup  of  tea,  does  its  dissolving  affect  the 
temperature  of  the  tea  in  any  way?    Explain. 

11.  If  you  had  some  powdered  alum,  how  would  you  make  good- 
sized  alum  crystals  out  of  it? 


CHAPTER  VI 

ELEMENTS  AND  COMPOUNDS 

98.  Physical  and  Chemical  Changes. —  If  we  heat  a 
flat-iron  on  a  stove,  it  becomes  hot.  It  may  even  become 
red  hot,  so  that  it  gives  off  heat  and  light.  But  if  it  is 
taken  from  the  stove,  it  becomes  cold  again,  and  looks 
just  as  it  did  before  the  heating.  A  lump  of  coal  thrown 
into  the  air  comes  down  again,  still  a  lump  of  coal.  The 
water  of  the  ocean  is  changed  into  steam,  then  carried 
away  by  air  currents,  and  finally  falls  again  as  rain  or 
snow.  The  iron  is  changed  in  temperature,  the  coal  and 
water  are  changed  in  position,  and  the  water  is  changed  in 
physical  state  (cf.  §  69);  but  the  changes  do  not  really 
alter  the  iron,  coal,  and  water.  We  call  such  changes 
physical  changes. 

But  if  a  piece  of  iron  is  left  in  moist  air,  it  rusts  (cf. 
§  48) .  If  water  is  added  to  quicklime ,  it  combines  with  the 
lime,  forming  "slaked"  lime;  it  is  no  longer  water.  If 
coal  is  burned,  it  disappears,  as  carbon  dioxide  and  steam 
(cf.  §  52).  Such  changes  do  alter  the  nature  of  substances. 
They  are  called  chemical  changes,  because  they  are  stud- 
ied in  the  science  of  Chemistry.  Chemical  changes  are 
also  called  reactions. 

Digestion  consists  of  the  physical  and  chemical  changes 
that  take  place  in  food,  in  order  that  it  may  be  taken  up 
by  the  blood  for  the  use  of  the  body. 

94 


ELECTROLYSIS  OF  WATER 


95 


99.  Composition  of  Water. —  By  the  "  composition/ ' 
or  " make-up,"  of  water  we  do  not  mean  a  list  of  the 
materials  present  in  a  particular  sample  of  water,  such  as 
the  carbon  dioxide,  limestone,  salt,  etc.,  that  are  dissolved 
in  a  natural  water  (cf.  §  80).  What  we  mean  is  that  pure 
water,  which  we  obtain  by  purifying  natural  water,  is 
still  made  up  of  two  different  substances :  hydrogen  and 
oxygen.  We  say  that  water  is  "composed  of,"  or  "is  a 
compound  of,"  hydrogen  and  oxygen. 

Water  is  formed  when  hydrogen  is  burned  (cf.  §§52 
and  105).  Can  we  reverse  the  action  that  takes  place  in 
burning,  and  break  up  water  into  hydrogen  and  oxygen, 
just  as  we  "decomposed"  mercury  oxide  into  mercury 
and  oxygen  (cf.  §  50)?  Water,  like  mercury  oxide,  can  be 
broken  up  by  heat;  but  the  temperature  required  is  very 
high,  and  the  method  is  hard  to  carry  out.  The  decom- 
position of  water  is  easy,  if  we  use  the  electric  current. 
The  operation  is  called  the  electro- 
lysis of  water.  Electrolysis  means 
"loosing,"  or  "breaking  apart,"  by 
the  use  of  electricity. 


100.  Electrolysis  of  Water.— The 

"breaking  apart"  of  water  by  the 
electric  current  may  be  carried  out 
as  follows  (Fig.  77)  :— 


FIG.  77. 

Electrolysis  of  Water.  The 
electric  current  breaks  up 
water,  containing  a  little 
of  an  acid,  into  hydrogen 
and  oxygen. 


Two  wires  from  a  battery  or  other  source 
of  the  current  (cf.  §§150  and  160)  pass  into  a 
vessel.  The  vessel  contains  water  and  a  very 

little  sulphuric  acid.    The  liquid  to  be  changed  by  the  electric  current 
is  thus  a  very  dilute  sulphuric  acid.    The  wires  inside  the  vessel  are 


96  ELEMENTS  AND  COMPOUNDS 

of  the  metal  platinum  (c/.  §  9),  and  they  have  tips  of  platinum  foil. 
We  call  the  ends  of  the  wires  the  poles  of  the  battery.  If  we  were  to 
put  the  two  platinum  poles  together,  the  current  would  have  a  com- 
plete passageway,  or  circuit,  without  going  through  the  dilute  acid. 
But  if  we  keep  the  poles  apart,  the  current  is  compelled  to  pass 
through  the  dilute  acid.  In  the  language  of  the  electrician,  the  dilute 
acid  makes,  or  doses,  the  circuit. 

While  it  is  carrying  the  current  from  one  pole  to  the  other,  the 
dilute  acid  is  changed  chemically  (cf.  §  98).  What  we  see  is  that 
bubbles  of  gas  arise  from  the  poles.  We  can  collect  the  gas  by  placing 
over  each  pole  a  test  tube  filled  with  some  of  the  dilute  acid.  We  then 
see  that  one  test  tube  collects  gas  about  twice  as  rapidly  as  the  other. 
If  we  put  a  burning  splinter  into  the  gas  that  is  collected  the  more 
slowly,  the  splinter  burns  more  brightly  than  in  air,  and  if  the  splinter 
is  merely  glowing,  it  will  burst  into  flame.  The  gas  collected  in  this 
tube  is  oxygen.  If  we  bring  a  flame  near  the  other  gas,  the  gas  takes 
fire  with  a  slight  "pop,"  or  explosion,  and  then  burns  with  an  almost 
invisible  blue  flame.  This  gas  is  hydrogen.  It  is  so  called  because 
it  is -a  part  of  water.  The  Greek  word  for  water  —  ' '  hydor  " —  appears 
in  many  other  English  words,  such  as  hydra,  hydrant,  hydraulic,  etc. 

101.  Elements  and  Compounds. —  Water  is  so  hard 
to  decompose  by  heat  that  men  were  unable  to  learn  its 
real  nature  until  1781.  In  that  year  Cavendish,  who  had 
prepared  hydrogen  in  1766,  burned  hydrogen,  and  ob- 
tained water.  The  decomposition  of  water  by  the  electric 
current  was  first  carried  out  in  1800.  The  question  now 
arises :  ' '  Can  the  hydrogen  and  the  oxygen  obtained  from 
water  be  divided  up  into  other  substances?'7  The  answer 
is  that  they  have  never  been  divided  by  any  method  used 
for  the  purpose.  A  substance  like  water,  which  is  not  a 
single  kind  of  matter,  but  has  at  least  two  kinds  of  matter 
in  it,  is  called  a  compound.  A  kind  of  matter  which  we 
have  never  been  able  to  break  up  is  called  a  simple 


MIXTURES 


97 


substance,  or  element.  Hydrogen,  oxygen,  nitrogen, 
carbon,  iron,  tin,  mercury,  etc.,  are  elements  (see  Appen- 
dix, Table  IX). 

How  complete  the  change  is,  when  substances  unite  chemically,  is 
seen  when  we  compare  water,  the  compound,  with  the  two  elements 
that  make  it  up.  The  formation  of  carbon  dioxide  by  the  burning  of 
carbon  is  another  common  illustration  of  the  same  thing.  No  one 
would  suspect  that  this  colorless  gas  (cj.  §  51),  which  puts  out  fire, 
which  is  exhaled  from  our  lungs,  and  is  taken  up  by  plants  (cf.  §  58), 
is  really  the  black  carbon  of  coal  and  charcoal,  and  of  the  "black  lead" 
of  our  pencils,  combined  with  the  active  gas  oxygen.  Yet  this  is 
the  case. 


102.  Mixtures. —  If,  in  the  electrolysis  of  water,  we 
were  to  collect  two  test  tubes  of  hydrogen  and  one  of 
oxygen,  and  were  to  mix  them  in  a  bottle  over  mercury 
(Fig.  78),  would  they  unite  at  once  to  produce  water? 
They  would  not.  They  would 
remain  in  each  other's  presence 
for  a  long  time  without  any 
noticeable  change.  It  is  neces- 
sary for  the  temperature  to  be 
raised  to  about  620°  C.  before 
the  two  gases  unite  rapidly. 
When  they  are  mixed  at  the 
ordinary  temperature,  they  form 
only  a  physical,  or  mechanical, 
mixture.  No  heat  is  set  free; 
no  new  substance  is  formed.  If  we  shake  the  mixture  with 
water,  the  hydrogen  dissolves  as  if  no  oxygen  were  present, 
and  the  oxygen  dissolves  as  if  no  hydrogen  were  present. 


FIG.  78. 

A  gas  can  be  transferred  from  one 
vessel  to  another  under  a  liquid. 


98 


ELEMENTS  AND  COMPOUNDS 


The  air  is  a  physical  mixture  of  nitrogen,  oxygen,  steam, 
carbon  dioxide,  and  small  amounts  of  other  gases. 

Of  course  we  have  mixtures  of  compounds,  as  well  as  of 
elements.  Natural  water  is  always  a  mixture  (cf.  §  80). 
All  soils,  and  most  rocks,  are  mixtures  (cf.  §§  285  and  294). 
The  forms  in  which  the  solid  elements  and  compounds 
are  found  in  nature  are  called  minerals. 


103.  Preparation  of  Hydrogen. —  The  most  common 
way  to  prepare  hydrogen  is  to  bring  certain  metals  and 
certain  acids  together.  All  acids  are  compounds  con- 
taining hydrogen  (cf.  §  214) ;  but  all  do  not  give  it  off  with 
the  same  ease.  The  best  acids  to  use  are  dilute  sulphuric 
acid  and  dilute  hydrochloric  acid;  the  best  metals  are 
zinc  and  iron. 

The  apparatus  needed  (Fig.  79)  is  a  bottle  provided  with  a  stopper 
having  two  holes,  a  "  thistle  tube,"  and  a  delivery  tube  reaching  to  a 


O 


FIG.  79. 
(A)  Making  Hydrogen  and  Collecting  It  over  Water. 


(B)  Collecting  It  over  Air. 


water-pan.  The  thistle  tube  is  the  opening  through  which  fresh 
supplies  of  acid  are  put  into  the  bottle;  it  also  allows  the  hydrogen  to 
escape  if  the  delivery  tube  becomes  stopped  up.  Hydrogen  is  not  very 


BURNING  OF  HYDROGEN 


99 


FIG.  80. 

Soap  Bubbles  Filled  with 
Hydrogen. 


soluble  in  water  (cf.  §  100),  and  is  collected  "over  water,"  just  as 
oxygen  and  nitrogen  are. 

104.  Properties  of  Hydrogen. —  Like  oxygen  and  nitro- 
gen, hydrogen  has  no  odor,  taste,  or  color.    It  is  the  light- 
est substance  known.    Oxygen  is  16  times  as  heavy  as 
hydrogen,    and    nitrogen    is    14 

times  as  heavy.  At  the  ordinary 
temperature  and  pressure  1  gram 
of  hydrogen  has  a  volume  of 
about  12  liters,  i.  e.,  about  3  gal- 
lons (cf.  Appendix,  Table  IV). 
Because  of  its  lightness,  hydrogen 
may  be  collected ' '  over  air  "  (Fig. 
79,  B),  and  may  be  used  to  fill 
balloons.  Soap  bubbles  filled  with  the  gas  rise  in  air 
(Fig.  80). 

105.  Burning  of  Hydrogen. —  If  we  wish  to  burn  hydro* 
gen  in  a  jet  (Fig.  81),  we  must  light  it  with  great  care. 

When  we  begin  the  prep- 
aration of  hydrogen,  the 
bottle  is  full  of  air;  hence 
the  first  portions  of  gas 
that  come  off  are  a  mix- 
ture of  hydrogen  and  air. 
If  we  light  this  mixture, 
there  will  be  a  violent  ex- 
plosion, which  may  break 
the  bottle,  and  blow  the 

FIG.  81.  . 

Hydrogen  burns  in  air  to  form  water.  glaSS  into  OUr  laCCS. 


100  ELEMENTS  AND  COMPOUNDS 

Before  we  bring  a  flame  near  a  jet  of  hydrogen,  we  hold  a  test  tube 
-over  the  outlet  tube  (Fig.  79,  B)  for  a  minute,  and  then  carry  the  test 
tube,  with  its  mouth  downward,  to  a  flame  at  least  3  feet  away.  The 
gas  in  the  test  tu*be  burns  rapidly,  if  it  still  contains  air;  but  if  it  con- 
sists of  fairly  pure  hydrogen,  it  burns  slowly.  When  we  have  lighted 
the  gas  in  the  test  tube,  we  carry  the  tube,  with  its  mouth  downward, 
back  to  the  jet  of  hydrogen.  We  do  this  until  the  test  tube  of  burn- 
ing hydrogen  sets  the  jet  of  hydrogen  on  fire. 

Hydrogen  burns  with  a  colorless  flame  when  pure. 
The  flame  is  very  hot.  When  1  gram  of  hydrogen  is  burned 
in  oxygen,  the  heat  given  off  is  sufficient  to  heat  342  grams 
of  water  from  0°  C.  to  100°  C. 

Water  is  formed  not  only  when  hydrogen  itself  burns, 
but  also  when  compounds  of  hydrogen  burn  (cf.  §  52). 
Thus  it  happens  that  when  a  kettle  of  cold  water  is  placed 
over  a  gas  flame,  water  drops  are  deposited  on  the  outside 
of  the  kettle.  When  the  kettle  becomes  hot 
enough,  the  steam  formed  in  the  burning 
escapes  without  being  condensed. 

106.  Diffusion  of.  Gases  and  of  Liquids. — 

If  we  attach  a  porous  cup  (Fig.  82)  tightly 
to  a  tube  ending  under  water,  and  place  a 
jar  of  hydrogen  over  the  cup,  an  interesting 
Hydrogen2 'pas-     phenomenon  takes  place :  bubbles  of  gas  escape 
Peo  r  lnu°s  cup     from  the  bottom  of  the  tube.   The  bottom  of  the 
S.arn  S^wS     jar  containing  hydrogen  is  open;  so  the  only 
reason  why  gas  escapes  through  the  water 
must  be  that  hydrogen  enters  the  porous  cup.    It  can  be 
proved  that  air  passes  outward  through  the  porous  materi- 
al; but  it  does  this  so  much  more  slowly  than  the  hydrogen 
goes  inward  that  there  is  a  sudden  increase  in  the  volume 


EXERCISES 


roi 


Hydrogen 


of  gas  inside  the  cup  and  tube.     Hence  some  of  it  es- 
capes through  the  tube. 

This  experiment  shows  that  gases  have  the  ability  to 
mix  when  placed  together.  We  call  this  mixing  diffusion, 
and  we  explain  it  by  saying  that  the  energy  of  the  molecules 
(cf.  §  61)  causes  the  molecules  of  the  one  gas  to  move 
rapidly  into  the  spaces  between  the  molecules  of  the 
other  gas,  until  the  mixing  is  complete. 

If  we  place  a  bottle  of  hydrogen,  with  its  mouth  downward  (Fig. 
83),  over  a  bottle  of  air,  the  hydrogen  diffuses  downward,  and  the  air 
upward,  in  spite  of  the  fact  that  air  is  14.4  times  as  dense 
as  hydrogen.     When  the  gases  are  separated  by  a  wall 
through  which  they  can  pass,  as  in  the  porous  cup  ex- 
periment, they  still  diffuse  into  each  other;  but  we  can 
see  that  they  move  at  different  rates:  the  lighter  gas 
diffuses  more  rapidly  than  the  heavier  one. 

Liquids  and  solutions  diffuse,  in  spite  of  gravity,  just 
as  gases  do.  Thus,  if  some  blue  vitriol  (cf.  §  95)  is  put 
into  the  bottom  of  a  tall  jar,  under  a  deep  layer  of  water, 
the  blue  vitriol  solution  that  is  formed  at  the  bottom 
rises  gradually  to  the  top,  coloring  all  the  water.  Also, 
if  some  alcohol  is  put  upon  water,  it  descends  into  the 
water,  even  though  the  water  is  the  heavier;  and  water 
ascends  into  the  alcohol,  until  the  mixture  is  complete. 

The  diffusion  of  oxygen  inward,  through  the  walls  of 
the  blood-vessels,  into  the  blood,  and  of  carbon  dioxide 
outward  causes  the  exchange  of  gases  necessary  for  the 
life  of  the  higher  animals  (cf.  §  52). 

107.  Exercises. 

1.  Are  the  following  changes  physical  or  chemical? — Souring  of 
milk,  freezing  of  water,  decomposition  of  mercury  oxide  by  heat,  dis- 
solving of  sugar  in  water,  incandescence  (" getting  white  hot")  of  an 
electric  light,  burning  of  candy  on  a  stove,  heating  a  penny  by  striking 


FIG.  83. 
Hydrogen 
passes  down- 
ward  into 
the  air,  and 
air  upward 
into  the  hy- 
drogen,. 


102  ELEMENTS  AND  COMPOUNDS 

it  with  a  hammer,  changing  of  the  starch  of  a  cracker  to  sugar  by  means 
of  the  saliva  in  the  mouth. 

2.  Compare  the  properties  of  hydrogen  with  those  of  oxygen. 
Compare  hydrogen  with  water. 

3.  What  properties  of  hydrogen  and  of  oxygen  can  you  show  only 
by  changing  these  elements  chemically? 

4.  In  what  proportions  by  volume  would  you  expect  hydrogen  and 
oxygen  to  unite  in  forming  water? 

5.  Coal,  wood,  and  kerosene  contain  carbon  and  hydrogen.    What 
products  are  formed  when  they  burn? 

6.  How  would  you  prove  that  wood  ashes  are  a  mixture  of  soluble 
and  insoluble  substances? 

7.  If  you  were  making  the  hydrogen  for  filling  a  balloon,  which 
would  be  the  cheaper  to  use  as  the  metal,  zinc  or  iron  (§  103)?    For 
what  reason  would  illuminating  gas  be  better  than  hydrogen?    In 
what  way  would  hydrogen  be  better? 

8.  How  many  calories  of  heat  are  given  off  when  1  g.  of  hydrogen 
burns  (§  105)? 

9.  Carbon  dioxide  is  1.5  times  as  dense  as  air.    If,  in  the  porous  cup 
experiment  (§106),  you  were  to  surround  the  cup  with  a  jar  of  carbon 
dioxide,  which  would  pass  through  the  porous  wall  more  rapidly,  the 
air  or  the  carbon  dioxide?    Would  air  be  forced  out  of  the  tube,  or 
would  water  be  forced  in? 

108.  Salt.  —  Salt   is   found   in   large   amount   in   sea 
water;  it  is  also  mined  as  rock  salt.    To  purify  rock  salt 

we  add  water  to  it,  so  that  the 
salt  dissolves,  while  the  impuri- 
ties do  not.  The  water  is  then 
boiled  off,  either  at  ordinary 
FIG.  84.  pressure  or  in  "vacuum  pans" 


Hopper-shapjdtMassof  Salt  fa    §  QQ).       ^dlt  Wells  form  an- 

other  source  of  salt. 

Salt  crystallizes  in  cubes  (§95);  masses  of  the  crystals 
are  "hopper  shaped"  (Fig.  84).    Because  the  crystals  do 


SODIUM  103 

not  fit  exactly  together,  some  of  the  brine  is  caught  be- 
tween them.  When  the  salt  crystals  are  heated,  some  of 
the  water  is  changed  to  steam,  and  bursts  the  crystal  mass. 
Hence  small  salt  crystals  " crackle "  when  heated;  while 
large  ones  "snap"  vigorously,  and  fly  out  of  the  dish. 

Salt  is  not  changed,  even  when  heated  to  fed  heat.  At 
white  heat  it  melts.  Like  water,  it  can  be  broken  up  by 
the  electric  current.  When  the  current  is  passed  through 
melted  salt,  its  elements,  sodium  and  chlorine,  are  formed, 
one  at  each  pole.  The  chemical  name  of  salt  is  sodium 
chloride. 

109.  Sodium. —  Sodium  is  a  metal,  like  silver,  gold, 
copper,  etc.;  but  it  is  so  soft  that  it  can  be  cut  with  a 
knife.  When  it  is  freshly  cut,  its  surface  is  white  as 
silver ;  but  it  is  soon  tarnished  by  the  moisture,  the  oxygen, 
and  the  carbon  dioxide  of  the  air.  Sodium  is  kept  under 
gasoline,  or  some  other  liquid  containing  no  oxygen. 
When  heated  in  air  or  oxygen,  sodium  burns,  forming 
sodium  oxide  (cf.  §§48  and  51). 

Sodium  acts  vigorously  with  water  (Fig. 
85) .  The  action  produces  so  much  heat  that 
the  sodium  melts,  forming  a  round  ball 
which  floats  upon  the  water.  A  gas  escapes 
with  a  hissing  noise,  and  the  sodium  finally 


disappears.      The  gas  produced  is  hydrogen.        FlQ.  85. 
When  the  water  is  rubbed  between  the  fin-   ^p^wlte^ 
gers,  it  feels  soapy,  or  slimy.     It  contains 
sodium  hydroxide,   also  called  caustic    (i.  e.,  burning) 
soda  (cf.  §  218). 

Sodium + water  give  sodium  hydroxide + hydrogen. 


104  ELEMENTS  AND  COMPOUNDS 

Owing  to  the  danger  that  sodium  may  be  spattered  into  our  eyes,  we 
never  put  more  than  a  very  small  piece  at  a  time  upon  water,  and 
we  add  it  at  arm's  length,  holding  a  piece  of  glass  between  our  eyes  and 
the  dish.  An  excellent  way  is  to  use  a  small  wide-mouth  bottle  3/4 
full  of  water  (Fig.  85).  The  bottle  is  provided  with  a  glass  cover, 
which  is  drawn  aside  when  the  sodium  is  added,  and  replaced  during 
the  action.  Several  pieces  of  sodium  may  be  added,  one  at  a  time. 
The  hands  and  tongs  used  must  be  dry.  If,  after  each  piece  of  sodium 
has  disappeared,  we  apply  a  match  to  the  mouth  of  the  bottle,  the  hy- 
drogen will  burn.  All  sodium  compounds  make  a  colorless  flame  yellow. 

110.  Chlorine. —  While  the  element  sodium  is  a  solid 
at  the  ordinary  temperature,  chlorine,  the  other  element 
present  in  salt,  is  a  gas.  The  gases  we  have  studied  up 
to  this  time  are  colorless,  odorless,  and  tasteless;  but 
chlorine  has  a  green  color,  a  suffocating  odor,  and  a  dis- 
agreeable action  on  the  lining  of  the  nose  and  throat.  It 
produces  the  effects  of  a  bad  cold.  Its  name  comes  from 
chloros,  the  Greek  word  for  "  green."  We  have  the  same 
word  in  "chlorophyll,"  the  green  coloring  matter  of 
plants  (cf.  §309). 

Chlorine  has  the  power  of  bleaching;  that  is,  of  removing 
the  color  of  grass,  straw,  and  other  plant  products.  It  also 
bleaches  cloth  or  paper  dyed  with  indigo,  litmus,  cochineal, 

etc.     Large  quantities  of 
chlorine  are  used  in  mak- 
ing bleaching  powder 
FIG.  so.  ("chloride  of  lime")'  an(l 

The  Bleaching  of  Cotton  Goods.  ,,          ,.  ,     ..  -m 

bleaching  solutions.  These 

are  used  for  the  whitening  of  cotton  goods  (Fig.  86) 
and,  as  "disinfectants,"  for  destroying  disease  germs. 
Bleaching  solutions  are  also  used  to  remove  ink  and 
other  stains  from  fabrics  (cf.  §  230). 


AMMONIA 


105 


When  a  burning  splinter  is  put  into  chlorine,  it  does  not  continue 
to  burn.  Many  metals,  however,  burn  vigorously  in  chlorine.  Thus, 
warm  copper  foil  takes  fire,  and  burns  to  form  copper  chloride.  If  thin 
shavings  of  sodium  are  put  into  chlorine,  the  sodium  becomes  covered 
with  a  white  deposit  of  common  salt,  and  is  soon  used  up.  We  thus 
prove,  both  by  breaking  up  salt,  and  by  forming  it  again,  that  it  is 
a  compound  of  sodium  and  chlorine. 

111.  Hydrochloric  Acid. —  When  a  jet  of  burning  hydro- 
gen (cf.  §  105)  is  put  into  a  bottle  of  chlorine  (Fig.  87),  the 
hydrogen  continues  to  burn,  and  the 
chlorine  disappears.  Instead  of  chlorine, 
the  bottle  now  contains  hydrogen  chlo- 
ride. This  is  a  colorless  gas.  It  fumes, 
or  "smokes,"  when  exposed  to  moist 
air,  and  forms  a  dense  fog  when  you 
blow  your  breath  over  it.  Hydrogen 
chloride  is  very  soluble  in  water;  the 
solution  is  hydrochloric  acid  (c/.  §214).  Hydrogen  bums  in 

»  i  ~i  f         .      .  •     .  •  •  j  chlorine  to  give   hy- 

An  old  name  for  it  is  muriatic  acid.  drogen  chloride. 


112.  Ammonia. —  The  two  elements  nitrogen  and  hy- 
drogen form  a  compound  called  ammonia.  This  is  a 
colorless  gas,  which  dissolves  readily  in  water,  forming 
"ammonia  water"  or  "aqua  ammonice."  Ammonia 
water  has  the  sharp  odor  of  ammonia  itself. 

Ammonia  water  is  one  of  the  bases  (cf.  §  218).  When 
a  bottle  of  "strong"  ammonia  water  and  one  of  "strong" 
hydrochloric  acid  are  brought  together,  the  gases  that 
arise  from  the  solutions  unite  to  form  a  white  cloud  of 
ammonium  chloride,  or  "sal  ammoniac"  (Fig.  88). 
This  is  the  white  solid  used  in  making  the  solutions 


106 


ELEMENTS  AND  COMPOUNDS 


for  the  batteries  that  ring  electric  door-bells,  etc.   (cf. 

§  152).  The  same  substance  is  formed  in  solution,  when 

ammonia  water  and  hy- 
drochloric acid  are  put 
together.  Here  we  have 
an  illustration*  of  the 
uniting  of  two  com- 
pounds to  form  a  more 
complex  compound. 


FIG.  88. 

Gaseous  ammonia  and  hydrogen  chloride  give 
white  fumes  of  sal  ammoniac.  After  Mellor's 
Chemistry.  Courtesy  of  the  publishers, 
Messrs.  Longmans,  Green  &  Co. 


113.  Sulphur.— Sul- 
phur, or  "brimstone/' 
is  another  element.  It 
does  not  dissolve  in  water ;  but  it  dissolves  in  carbon  di- 
sulphide  (cf.  §  95).  When  the  solution  is  allowed  to 
evaporate  slowly,  crystals  of  sulphur  are  obtained  (Fig. 
3).  Carbon  disulphide  must  be  evaporated  away  from 
a  fire,  as  it  is  very  inflammable. 

Sulphur  is  found  chiefly  in  volcanic  regions  such  as  in 
Sicily,  Mexico,  and  Japan.  Louisiana  now  produces 
more  than  any  other  state,  and  as  much  as  Sicily. 

Sulphur  burns  in  air  or  oxygen  to  give  the  colorless, 
suffocating  gas,  sulphur  dioxide  (cf.  §  51).  This  is  used 
to  bleach  straw,  silk,  lace,  wool,  etc.,  which  would  be  in- 
jured by  chlorine  (cf.  §  110).  It  is  also  used  to  destroy 
the  germs  of  disease,  and  vermin,  such  as  fleas.  We  make 
the  gas  for  this  purpose  by  burning  sulphur  "candles,"  or 
by  pouring  liquid  sulphur  dioxide  (cf.  §  71)  into  saucers, 
and  allowing  it  to  evaporate. 

Hydrogen  and  sulphur  form  the  compound  hydrogen  sulphide. 
This  is  a  gas  having  the  disgusting  odor  of  rotten  eggs.  When  eggs 


NUMBER  OF  ELEMENTS  AND  COMPOUNDS 


107 


decay,  part  of  the  hydrogen  and  sulphur  they  contain  is  given  off  as 
hydrogen  sulphide.  The  gas  burns  in  air,  giving  water  and  sulphur 
dioxide  (cf.  §  105).  It  is  present  in  the  mineral  waters  known  as 
"sulphur"  waters. 

114.  Number    of    Elements    and    Compounds. —  The 

total  number  of  compounds  known  is  very  large :  probably 
several  hundred  thousand.  All  of  these  are  made  out  of 
80  or  90  elements.  Most  com- 
pounds contain  only  2,  3,  or  4 
of  these  elements,  and  only 
about  30  elements  are  at  all 
common  (Fig.  89).  We  may 
compare  the  formation  of  com- 
pounds out  of  elements  with  the 
making  of  the  many  words  of 
our  language  out  of  its  26  let- 
ters. In  the  following  table  Abundance  of Eements  in  the 
we  have  the  names  of  some 

compounds  formed  out  of  the  elements  we  have  been 
studying. 


Combined 
with 

Oxygen 

Nitrogen 

Carbon 

Chlorine 

Sulphur 

Hydrogen 

Water 

Ammonia 

Marsh 
gas 

Hydrogen 
chloride 

Hydrogen 
sulphide 

Oxygen 

Nitrogen 
oxide 

Carbon 
dioxide 

Chlorine 
oxide 

Sulphur 
oxide 

Nitrogen 

Nitrogen 
oxide 

Cyanogen 

Nitrogen 
chloride 

Carbon 

Carbon 
dioxide 

Cyanogen 

Carbon 
chloride 

Carbon 
disulphide 

Chlorine 

Chlorine 
oxide 

Nitrogen 
chloride 

Carbon 
chloride 

Sulphur 
chloride 

Sodium 

Sodium 
oxide 

Sodium 
nitride 

Sodium 
carbide 

Sodium 
chloride 

Sodium 
sulphide 

108  ELEMENTS  AND  COMPOUNDS 

115.  Summary. — Physical  changes  do  not  alter  the  nature  of  a 
substance;  chemical  changes  do. 

Water  is  composed  of  hydrogen  and  oxygen. 

The  electrolysis  of  water  gives  two  volumes  of  hydrogen  for  one  of 
oxygen. 

Elements  are  substances  that  have  never  been  divided. 

Compounds  are  made  up  of  elements  that  are  united  as  the  result  of 
a  chemical  change. 

Mixtures  are  made  up  of  elements  or  compounds  not  united  chemi- 
cally. 

Hydrogen  is  prepared  by  the  action  of  certain  metals  upon  certain 
acids.  It  is  the  lightest  substance  known. 

Hydrogen  burns  with  a  very  hot  flame,  forming  water.  Water  is 
also  formed  in  the  burning  of  compounds  of  hydrogen,  such  as  wood 
and  coal. 

Diffusion  is  the  mixing  of  substances  because  of  molecular  motion. 

Salt  is  sodium  chloride.  It  is  broken  up  by  electrolysis  into  sodium 
and  chlorine. 

Sodium  is  a  metal,  which  burns,  and  which  acts  upon  water.  It 
reunites  with  chlorine,  giving  salt. 

Chlorine  is  a  green  gas,  which  has  the  power  of  bleaching  and  dis- 
infecting. Ordinary  combustibles  do  not  burn  in  it. 

Hydrogen  burns  in  chlorine,  giving  hydrogen  chloride.  In  solution 
this  is  hydrochloric  acid. 

Ammonia  is  a  compound  of  nitrogen  and  hydrogen.  It  unites  with 
hydrogen  chloride  to  give  ammonium  chloride,  or  "sal  ammoniac." 

Sulphur  burns  to  give  sulphur  dioxide.  Hydrogen  sulphide  is 
formed  by  the  decay  of  organic  materials  containing  sulphur,  such 
as  eggs. 

The  number  of  compounds  is  very  large ;  but  most  of  them  are  made 
out  of  only  2,  3,  or  4  elements. 

116.  Exercises. 

1.  What  are  the  melting  points  of  the  following  metals :  sodium,  tin, 
lead,  copper,  silver,  gold,  cast  iron,  steel?  (See  Appendix,  Table  V.) 


EXERCISES  109 

2.  Look  up  the  densities  of  the  following  metals:    sodium,  alu- 
minum, iron,  lead,  gold.     Is  sodium  heavier  than  water? 

3.  Bromine  is  an  element  similar  to  chlorine.     Give  the  name  of  the 
compound  it  forms  with  sodium,  with  hydrogen,  with  carbon,  and 
with  sulphur. 

4.  When  a  jet  of  hydrogen  issuing  from  a  glass  tube  is  first  lighted, 
its  flame  is  colorless  and  invisible;  but  when  the  glass  becomes  hot,  the 
flame  is  yellow.     What  element  forms  a  part  of  glass? 

5.  When  common  salt  is  treated  with  concentrated  sulphuric  acid, 
hydrogen  chloride  is  formed.    Where  does  its  hydrogen  come  from? 
Its  chlorine? 

6.  What  compounds  are  formed  when  carbon  disulphide  burns? 

7.  When  a  ton  of  soft  coal  is  heated,  it  gives  off  about  6  Ibs.  of 
ammonia.    What  elements  must  coal  contain? 


CHAPTER  VII 

CARBON  AND  ITS  COMPOUNDS 

117.  Carbon  as  an  Element. —  We  all  know  carbon  as 
it  exists  in  soot,  coal,  charcoal,  and  in  the  " black  lead" 
of  our  pencils.    It  is  a  black  solid;  it  does  not  dissolve  in 
water;  and  even  powerful  chemicals,  such  as  acids  and 
bases  (cf.  §  214),  do  not  change  it  to  any  great  extent. 
When  it  is  heated  to  the  right  temperature,  it  burns, 
forming  carbon  dioxide  (cf.  §  51).    It  is  hard  to  believe 
that  the  bright,  hard,  and  lustrous  diamond  (Fig.  75,  §  95) 
is  a  form  of  the  same  element  as  the  black  graphite  (' '  black 
lead")  and  charcoal,  yet  it  is  true.     If  a  pure  sample  of 
each  of  these  substances  is  completely  burned  in  oxygen, 
it  gives  nothing  but  carbon  dioxide.  If  a  diamond  is  heated 
in  a  tube  containing  no  oxygen,  it  is  changed  to  graphite. 

Carbon  is  of  great  importance  for  all  life  upon  the  earth. 
Living  things  are  made  up  of  wonderfully  constructed 
compounds  containing  carbon.  Proteids,  sugar,  starch, 
and  fats  are  such  compounds.  When  compounds  of  car- 
bon are  heated,  and  can  get  plenty  of  oxygen,  they  usually 
burn.  But  when  they  are  heated  without  sufficient  air, 
or  too  rapidly,  nearly  all  of  them  char,  or  "turn  to  car- 
bon." We  have  all  seen  this  happen  when  sugar  or  milk 
have  been  spilled  upon  a  hot  stove,  and  when  toast  or 
meat  have  been  "burned"  by  overheating. 

118.  Coal. —  All  of  the  many  different  kinds  of  coal 

110 


USES  OF  THE  FORMS  OF  CARBON 


111 


(Fig.  90)  were  probably  formed  from  vegetable  matter, 
such  as  leaves,  boughs,  trunks,  and  roots,  that  collected 


FIG.  90. 


Parallel  Seams  of  Coal  Outcropping  on  a  Hillside.     Clay  beds  lie  under  the  coal.     Here  the 
other  rock  is  sandstone;  often  it  is  limestone  as  well.     After  Hopkins. 

under  water  in  past  ages.  This  material  was  prevented 
from  decaying  by  deposits  of  sand  and  mud,  which  kept 
out  the  air  (cf.  §  38)  while  the  change  to  coal  was  going 
on.  In  some  imperfect  coals  the  markings  of  the  original 
wood  can  still  be  seen.  In  "soft,"  or  bituminous,  coals 
the  change  is  usually  more  complete,  but  many  carbon 
compounds  still  remain;  while  in  anthracite,  or  "hard," 
coal  the  change  of 
vegetable  matter  to 
coal  is  so  complete 
that  very  little  is 
present  besides  car- 
bon. See  Fig.  91.  ' 


119.  Uses  of  the 
Forms  of  Carbon. — 
The  element  carbon 
is  put  to  a  multitude 


YEAR 

SHORT  TONS 

TOO,  000,  000    200,000,000  300,000,000     400,000,000 

1814-1820 

424 

1821-18*0 

140,331 

1891-18*0 

1.031.642 

1841-1850 

14,534  58<j 

1851-1860 
1861-1870 

•  12,  513.  ( 

•  26,122, 

06 
Oil, 

1871-1880 

S^am   57 

219.992 

1881-1890 

ncanoBCBi 

•1122.  844 

,.666 

FIG.  91. 

Coal  Produced  Yearly  in  the  United  States.    Average 

by  10-year  periods.     Courtesy  of  Dr. 

F.  W.  De  Wolf. 


112 


CARBON  AND  ITS  COMPOUNDS 


of  uses  by  man.  Charcoal  made  from  wood  and  bones  is 
very  porous,  and  the  air  in  its  pores  is  able  to  destroy 
(oxidize)  many  natural  coloring  materials,  as  well  as  gases 

and  bacteria.  Charcoal 
(Fig.  92)  is,  therefore, 
used  to  take  the  color  out 
of  sugar  solution  and 
vinegar,  as  a  disinfectant 
(cf.  §  110),  and  as  a  ma- 
terial for  filters  (cf.  §84). 
Soot,  or  lampblack,  is 
FlG-92-  j  used  to  make  printer's 

Making  Charcoal  from  Wood.      Burning  part        . 

of  the  wood  gives  off  the  heat  necessary  ink,       black       Daint,       etc. 

to  char  the  remainder.  *  ; 

Gas  carbon  (cf.  §  124)  is 

used  for  the  carbon  "pencils"  of  electric  arc  lamps  and 
for  the  plates  of  electric  batteries  (cf.  §  150).  The 
diamond  is  used  not  only  as  a  jewel,  but  also  as  a 
cutting  and  polishing  material.  It  is  the  hardest  substance 
known.  Graphite  is  used  for  lead  pencils,  as  stove  polish, 
and  to  destroy  "boiler  scale"  (cf.  §  82). 

Charcoal,  coal,  and  coke  are  used  as  fuels,  and  to  reduce  the  ores 
of  iron  and  other  metals  (Fig.  93).  Most  of  the  metals  are  found  as 
oxides  (cf.  §  48),  or  as  compounds  that  can  be  changed  easily  into 
oxides.  When  the  oxide  of  the  metal  is  heated  with  carbon,  the  carbon 
unites  with  the  oxygen,  releasing  the  metal.  We  say  that  the  ore  is 
reduced  by  the  carbon.  Copper,  tin,  lead,  zinc,  etc.,  are  obtained  in 
this  way.  The  commercial  apparatus  for  reducing  the  ores  of  iron  is 
called  a  " blast  furnace"  (Fig.  94). 

120.  Hydrocarbons. —  There  are  thousands  of  sub- 
stances consisting  of  carbon  combined  with  other  ele- 
ments. Carbon  compounds  are  also  called  organic  com- 


HYDROCARBONS 


11$ 


FIG.  93. 

Charcoal  burns  with  a  very  hot  flame  in  a  rapid  current  of  air.     A  Blacksmith's  Forge. 

On  the  right  is  an  old  bellows  forge;  on  the  left  is  an  electric-power  blower 

forge.     Field  Museum  of  Natural  History,  Chicago. 


FIG.  94. 

Model  of  a  Blast  Furnace.     The  one  in  cross  section  shows  coarse  iron  ore,  limestone,. 

and  coke  (or  coal)  at  the  top;  below  this,  the  slag;  at  the  bottom,  molten  iron. 

The  blast  of  hot  air  enters  through  pipes  near  the  bottom. 

Field  Museum  of  Natural  History. 


114 


CARBON  AND  ITS  COMPOUNDS 


pounds  (cf.  §  3).    The  compounds  that  contain  only  car- 
bon and  hydrogen  are  called  hydrocarbons.    Among  them 

are  marsh  gas  and  acetylene  (cf. 
§§  158  and  257),  which  are  a  part 
of  illuminating  gas  (cf.  §  124). 
Another  important  hydrocarbon 
is  benzene,  a  colorless  liquid  ob- 
tained from  coal  tar. 


FIG.  95. 
Collecting  Marsh  Gas. 


Marsh  gas  gets  its  name  from  the 
fact  that  it  is  found  in  marshes  and 
pools.  It  is  formed  by  the  decay  of 
leaves  and  twigs  under  water.  If  the  bottom  of  a  pool  is  stirred 
with  a  stick,  bubbles  of  this  gas  usually  arise,  and 
may  be  collected  over  water  (Fig.  95). 

Marsh  gas  can  be  burned;  in  mines  it  is  called  fire 
damp.  When  there  is  much  of  it  mixed  with  the  air 
of  a  mine,  and  a  flame  is  brought  into  the  mixture  a 
violent  explosion  takes  place.  To  avoid  these  explo- 
sions, Sir  Humphry  Davy,  who  was  himself  a  miner 
when  a  boy,  invented  a  safety  lamp  (Fig.  96),  which 
could  be  taken  into  the  mixture  of  fire  damp  and  air 
without  setting  the  mixture  on  fire.  The  safety  lamp 

is  a  lamp  with  its  flame  entirely  surrounded 
by  wire  gauze. 

Natural  gas  is  a  mixture  of  hydrocarbons. 
It  is  chiefly  marsh  gas. 


FIG.  96. 

Modern  Form 

of  the  Miner's 

Safety  Lamp. 


Drill  Hole 


121.  Petroleum. —  Petroleum  is  a 
dark  liquid  obtained  from  oil  wells 
(Fig.  97).  It  is  a  mixture  of  hydro- 
carbons, some  gaseous,  some  liquid, 
and  some  solid.  If  we  were  to  distill  some  of  it,  we  would 
obtain,  first,  gases  we  could  not  condense,  then  liquids 


FIG.  97. 

How  Petroleum  is  Found 
in  the  Earth. 


FLASHING  POINT 


115 


BARRELS 
joo.ooo.ooo 


with  a  low  boiling  point,  then  liquids  with  a  higher  boil- 
ing point,  and  so  on.  Finally  there  would  remain  a  black, 
tarry  material. 

The  distillation,  or  refining,  of  petroleum  is  carried  out  on 
an  enormous  scale  (Fig.  98). 
The  portions  ("fractions") 
having  different  boiling 
points  are  collected  sepa- 
rately, and  are  known  by 
different  commercial  names. 
Some  of  them  are  gasoline, 
naphtha,  petroleum  ether, 
kerosene,  etc.  Some  of  the 
hydrocarbons  of  petroleum 
have  so  high  a  boiling  point 
that  they  char  before  they  distil, 
low  pressure,  "  vacuum  " 


I/ 

A 

& 

$ 

il 

1 

<{ 

3 

|£ 

\\ 

[ 

I 

1 

1 

^-— 

^ 

1L 

If 

1  I 


1  I  I 


FIG.  98. 

Amount  of  Petroleum  Produced  in  the 
United  States. 


These  are  distilled  in 
apparatus  (c/.  §  90),  just  as  the 
water  is  distilled  off  commercially  from  sugar  or  salt  solu- 
tion. Vaseline  is  a  high-boiling  material  obtained  from 
petroleum;  paraffin,  or  "white  wax,"  is  another.  A 
residue  of  coke  remains  when  petroleum  is  distilled.  More 
than  200  different  commercial  products  are  obtained  from 
petroleum. 


122.  Flashing  Point. — Kerosene,  which  is  used  in  lamps,  is  composed 
of  hydrocarbons  that  boil  at  a  moderately  high  temperature  (150°  C.  to 
250°  C.).  If  kerosene  contains  hydrocarbons  having  too  low  a  boiling 
point,  as  is  the  case  with  gasoline,  its  vapor  and  the  air  will  form  an 
explosive  mixture.  To  prevent  kerosene  explosions  governments 
insist  that  a  mixture  of  kerosene  vapor  and  air  shall  not  take  fire  below 
a  certain  temperature;  in  other  words,  that  the  kerosene  shall  have  a 
certain  "  flashing  point."  We  find  the  flashing  point  (Fig.  99)  by  put- 


116 


CARBON  AND  ITS  COMPOUNDS 


ting  a  tube  of  kerosene  into  a  vessel  of  water,  and  gradually  heating  the 
water.  At  the  same  time  we  force  air  bubbles  through  the  kerosene, 
with  the  result  that  a  froth  rises  to  the  mouth  of 
!==*-  the  tube.  When  the  froth  can  be  lighted  with 
a  match,  the  temperature  shown  by  the  ther- 
mometer is  the  flashing  point  of  the  kerosene. 
In  most  states  the  flashing  point  is  150°  F.,  or 
65°  C. 


Air  and 
Kerosene 
Vapor  V 


FIG.  99. 


123.  Other  Compounds  of  Carbon. — 
Carbon,  hydrogen,  and  oxygen  form  a 
large  number  of  compounds.  Among 
them  are  the  fats  and  sugars,  starch,  cellulose  (the 
material  of  wood,  cotton,  and  paper),  acetic  acid  (the 
acid  of  vinegar),  lactic  acid  (the  acid  of  sour  milk), 
ordinary  alcohol,  wood  alcohol,  ether,  etc. 

Carbon,  hydrogen,  and  nitrogen  form  aniline,  and  the 
poisonous  prussic  acid ;  while  carbon,  hydrogen,  nitrogen, 
and  oxygen  make  up  the  principal  part  of  all  living  tissue. 
These  compounds  of  carbon  are  studied  in  Organic  Chem- 
istry. 

124.  Dry  Distillation  of  Coal  and  Wood.— By  "dry 
distillation7'  we  mean  the  heating  of  solids,  and  the  col- 
lecting of  the  materials  that  distill  off.  It  is  not  a  physical 
change,  like  the  distillation  of  water 
(cf.  §  83) ;  because  the  solids  we  ' '  dry 
distill77  are  decomposed  in  the  pro- 
cess. When  coal  is  "distilled,"  gases, 
liquids,  and  solids  are  given  off,  and 
coke  and ' '  gas  carbon  "  remain  behind 
(cf.  §  119).  The  gases  are  known  as  illuminating  gas; 
they  are  chiefly  hydrocarbons  and  hydrogen.  Soft  coal 


FIG.  100. 
Dry  Distillation  of  Wood. 


CARBON  DIOXIDE  117 

contains  nitrogen   compounds,  hence  ammonia  is  also 
formed  (cf.  §  112). 

The  liquid  that  distils  off  from  coal  is  called  "coal  tar."  This  is  of 
great  commercial  importance,  for  it  contains  benzene,  aniline,  etc.,  out 
of  which  the  wonderful  coal  tar  dyes,  as  well  as  many  other  valuable 
substances,  are  made  (cf.  §  228). 

The  liquid  obtained  by  the  dry  distillation  of  wood  (Fig.  100) 
contains  wood  alcohol,  or  "wood  spirit,"  which  is  used  to  dissolve 
certain  gums,  such  as  shellac,  and  as  a  fuel.  Acetic  acid  is  also  formed 
(cf.  §  123). 

125.  Exercises. 

1.  Do  you  think  that  the  diamond  would  burn  with  a  flame? 
Why? 

2.  What  fuel  does  the  blacksmith  use  for  his  fire?    Why  does  he  use 
bellows? 

3.  Does  wood  charcoal  leave  ash  when  burned?    Does  coke?    Are 
these  pure  carbon?    Would  sugar  charcoal  leave  ash? 

4.  Is  it  possible  that  coal  is  being  formed  now?    Where?    What 
is  "peat"? 

5.  In  what  sense  does  coal  contain  the  stored-up  energy  of  the 
sun? 

6.  Turpentine  burns  with  a  smoky  flame,  while  the  flame  of  alcohol 
is  smokeless.    What  element  is  probably  present  in  turpentine?    How 
can  we  prove  that  the  same  element  is  present  in  alcohol? 

7.  Why  does  the  wire  gauze  of  the  safety  lamp  prevent  the  flame 
inside  from  setting  the  fire  damp  of  the  mine  on  fire? 

8.  Why  cannot  gasoline  be  burned  safely  in  a  lamp?    Why  cannot 
kerosene  be  used  in  place  of  gasoline  in  the  engine  of  an  automobile? 

126.  Carbon  Dioxide. —  Carbon  dioxide,  or  "carbonic 
acid  gas/'  is  formed  when  carbon  and  carbon  compounds 
(tf-  §§51  and  101)  burn  in  air  or  oxygen.    It  is  a  colorless 
gas  that  dissolves  slightly  in  water,  giving  the  water  a 
mildly  acid  taste.    The  solution  is  called  carbonic  acid. 


118 


CARBON  AND  ITS  COMPOUNDS 


If  the  carbon  dioxide  and  water  are  brought  together 
under  a  pressure  greater  than  that  of  the  atmosphere  (cf. 
§  41),  more  of  the  gas  dissolves  than  at  ordinary  pressure. 
Water  thus  "charged"  with  carbon  dioxide  is  called 
"soda  water."  When  soda  water  is  exposed  to  the  air, 
it  froths,  or  foams,  because  the  excess  of  dissolved  carbon 
dioxide  escapes.  This  escape  of  carbon  dioxide  causes  the 
effervescing,  or  frothing,  of  drinks  containing  it.  Water 
is  often  charged  with  carbon  dioxide  naturally,  below  the 
earth's  surface.  '  When  such  water  rises  to  the  surface, 
the  carbon  dioxide  escapes. 

Carbon  dioxide  does  not  burn;  neither  do  burning  bodies,  such  as  a 
candle  or  match,  continue  to  burn  when  put  into  it.  The  higher 
animals  do  not  continue  to  live  in  carbon  dioxide,  because  they  cannot 
live  without  free  oxygen;  they  cannot  get  the  oxygen  of  carbon  dioxide 
away  from  the  carbon. 

127.  Carbon  Dioxide  in  the  Air.—  Carbon  dioxide  gets 
into  the  air  from  all  ordinary  burning,  from  the  breathing 
of  animals  and  plants,  and  from  the  de- 
cay of  animal  and  vegetable  matter. 
We  can  test  the  air  for  carbon  dioxide 
by  exposing  to  the  air  a  shallow  dish  of 
lime  water,  which  is  a  solution  of  slaked 
lime  (cf.  §  132).  Or  we  can  draw  air 
through  lime  water  (Fig.  101).  There 
will  be  formed  a  scum,  or  a  precipitate, 
of  calcium  carbonate,  the  substance  that 
makes  up  marble  and  limestone. 

We  can  prove  that  there  is  carbon  dioxide  in  the  breath 
by  blowing  the  breath  through  lime  water.  The  same 
white  precipitate  is  formed. 


Suction 


FIG.  101. 

Drawing  Air  through 
Lime  Water. 


CARBON  DIOXIDE  IN  FERMENTATION 


119 


128.  To  Prepare  Carbon  Dioxide. —  When  marble  and 
soda  are  treated  with  a  dilute  acid,  carbon  dioxide  is  formed. 
Since  the  gas  is  only  slightly  soluble,  it  escapes.  It 
may  be  collected  over  water,  just  as  oxygen  and  hydrogen 
are  (cf.  §§50  and  103),  or,  since  it  is  1%  times  as  heavy  as 
air,  it  may  be  allowed  to  pour  out  of  the  delivery  tube 
(Fig.  102)  into  a  bottle  of  air.  In  a 
short  time  all  the  air  will  be  replaced  by 
carbon  dioxide.  We  can  prove  this  by 
putting  a  burning  match  into  the  bottle; 
the  match  will  "go  out." 

Carbon  dioxide  may  be  poured,  like 
water,  from  one  bottle  into  another. 


129.  Carbon    Dioxide  in 
tion. — When    fruit    juices, 


Fermenta- 
like    apple 


FIG.  102. 

The  carbon  dioxide  falls 
.     .  .     •  into  the  bottom  of  the 

juice  and  grape  juice,  stand  exposed  to  bottle,  and  pushes  the 
the  air,  they  "work,"  or  ferment.  If 
we  examine  the  fermenting  juice,  we  find  that  it  is 
warmer  than  the  surrounding  air,  that  a  gas  comes  off 
from  it,  and  that  the  sweet  taste  of  the  juice  is  changed 
to  the  taste  of  dilute  alcohol.  The  cause  of  the  fermenta- 
tion is  the  yeast  plant.  The  spores,  that  is,  seedlike  bodies 

(cf.  §  323),  of  wild  yeast  fall  into 
the  fruit  juice,  and  sprout,  and 
in  their  growth  change  the  sugar 
of  the  juice  into  alcohol  and 
carbon  dioxide  (Fig.  103). 

If  we  put  prepared  yeast  ("com- 
pressed" yeast  or  "dry"  yeast)  into  a 
dilute  solution  of  molasses,  the  fer- 


FIG.  103. 
Yeast  Cells  Budding. 


120  CARBON  AND  ITS  COMPOUNDS 

mentation  is  rapid.  In  three  or  four  days  the  liquid  can  be  distilled, 
and  alcohol  can  be  obtained  in  the  first  droppings  from  the  condenser. 
The  alcohol  comes  over  before  the  water  does  (cf.  §  83). 

When  bread  is  made,  carbon  dioxide  is  produced  by  the  action  of 
yeast  upon  sugar  and  flour,  and  causes  the  dough  to  rise.  The 
alcohol  vapor  also  assists;  but  both  alcohol  and  carbon  dioxide  are 
largely  expelled  in  the  baking. 

130.  Baking  Powders. —  Artificial  sources  of  carbon 
dioxide  are  used  to  "raise"  biscuits  and  cake;  these  are 
called    "  baking   powders."      Common   baking   powder 
contains  baking  soda,  cream  of  tartar,  and  starch.    The 
correct  proportion  is  two  parts  of  cream  of  tartar  to  one 
of  baking  soda.     The  soda  is  the  source  of  the  carbon 
dioxide,  just  as  the  marble  is  when  we  prepare  the  gas  in 
the  laboratory.    The  cream  of  tartar  is  the  acid.     The 
carbon  dioxide  passes  off  as  it  raises  the  dough,  while  the 
other  product  of  the  action,  sodium  potassium  tartrate, 
is  left  in  the  baked  article.     It  is  important  that  the 

•solid  substances  formed  by  baking  powder,  which  are 
left  in  the  food,  shall  not  be  harmful  to  the  persons  eat- 
ing them.  Acid  phosphate  baking  powders  contain  acid 
calcium  phosphate  instead  of  cream  of  tartar. 

131.  Carbon  Dioxide  as  a  Fire  Extinguisher. —  Since 
carbon  dioxide  does  not  permit  burning  to  continue,  it 
can  be  used  like  water  to  put  out  fires.    There  is  a  great 
advantage  in  using  it  if  the  fire  is  small,  for  the  carbon 
dioxide  does  not  damage  the  things  that  do  not  burn, 
while  water  does.     It  cannot  be  used  for  large  fires, 
because  it  cannot  be  put  into  the  burning  material  in 
large  enough  amounts.    A  chemical  engine  consists  of  a 
strong  vessel  in  which  carbon  dioxide  is  generated  from 


LIMESTONE 


121 


soda  and  a  dilute  acid.   When  the  stream  of  carbon  dioxide 
is  turned  upon  the  burning  object,  it  expels  the  air,  and 
as  there  is  then  no  free  oxygen,  the  fire  is  put  out.    Fire 
extinguishers  (Fig.  104)  of  various  sorts  con- 
tain about  the  same  materials  as  chemical 
engines. 

132.  Limestone. —  Limestone  is  found  in 
large  deposits,  usually  as  a  gray  solid.  It  is 
composed  of  carbon,  oxygen,  and  the  metal 
calcium.  Its  chemical  name  is  calcium  car- 
bonate. Limestone  is  insoluble  in  water;  but 
if  the  water  contains  carbon  dioxide  (cf.  § 
126),  the  limestone  dissolves  to  some  extent. 
When  thus  dissolved,  it  causes  the  temporary  hardness  of 
water  (cf.  §  82).  Water  containing  limestone  is  "broken" 


bottle,  sulphuric 
acid.  When 
these  substances 
react,  carbon  di- 
oxide is  formed. 


Fio.  105. 

Marengo  Cave,  Ind.     The  masses  hanging  from  the  ceiling  and  those  rising  from 
the  floor  are  both  deposited  by  water  that  drips  from  the  ceiling. 


122 


CARBON  AND  ITS  COMPOUNDS 


by  boiling  it.    This  drives  off  the  carbon  dioxide,  and  the 
calcium  carbonate  then  settles  out. 

Underground  water  charged  with  carbon  dioxide  wears  away 
limestone,  forming  caves.  Sometimes  these  are  very  large.  When, 
later,  water  containing  carbon  dioxide  and 
limestone  enters  a  cave,  the  carbon  dioxide 
usually  escapes,  and  the  dissolved  limestone 
is  deposited.  If  the  water  drips  from  the 
ceiling  of  the  cave,  each  drop  leaves  its  bit  of 
limestone  behind.  In  this  way  hanging  masses, 
called  stalactites,  are  formed.  The  limestone 
deposited  on  the  floor  forms  a  rising  column, 
called  a  stalagmite.  Often  the  two  join  to 
form  a  pillar  (cf.  Fig.  105). 

Marble  is  a  finely  crystallized  form 
of  limestone.  Limestone  makes  up  not 
only  large  rock  deposits,  but  also  the 
shells  and  hard  parts  (bones,  etc.)  of 

animals  (Fig.  106).    Enormous  deposits  of  limestone  (Fig. 

107)  are  formed  out  of  coral,  the  stony  framework  of  the 

coral  animal  (cf.  Fig.  257,  §  334). 


FIG.  106. 

Chalk,  as  magnified  by  a 
microscope.  _  Note  the 
tiny  shells  it  contains. 
Chalk  is  not  ordinary 
blackboard  crayon. 


FIG.  107. 
Eagle  Cliff,  Peninsula  Park,  Wisconsin.     Note  the  layer  formation  of  the  limestone. 


SUMMARY 


123 


Carbon  Dioxide 

~    t    ~ 


Lime- 
stone 


Lime 


When  limestone  is  heated  to  a  high  temperature,  it  is 
decomposed,  giving  lime  and  carbon  dioxide.  The  appara- 
tus is  called  a  lime  kiln  (Fig.  108).  Lime 
is  used  to  make  mortar  and  plaster.  It 
is  first  "slaked"  with  water,  and  the 
"milk  of  lime"  that  is  formed  is  mixed 
with  sand.  When  the  mortar  "sets,"  it 
takes  up  carbon  dioxide  from  the  air, 
forming  limestone  once  more.  This 
fastens  bricks  and  stones  firmly  together, 
and  we  call  it  mortar.  When  it  forms  a 
stony  covering  for  our  walls  we  call  it 
plaster. 

133.  Summary. — Carbon  exists  as  diamond,  graphite,  coal,  coke,, 
charcoal,  soot,  etc.;  also  as  one  of  the  elements  of  sugars,  starches, 
fats,  proteids,  and  of  living  creatures.  When  heated,  most  substances 
containing  carbon  are  charred. 

Coal  was  probably  formed  out  of  vegetation. 

Uses  of  carbon  are:  for  filters,  black  paints,  printer's  ink,  pencils, 
fuel,  etc.  Diamonds  are  used  as  jewels  and  as  cutting  materials. 
Carbon  is  the  element  used  to  reduce  the  ores  of  the  metals. 

Hydrocarbons  are  compounds  of  carbon  and  hydrogen. 

Petroleum  is  a  mixture  of  hydrocarbons  found  in  the  earth.  Dis- 
tillation of  petroleum  gives  gasoline,  kerosene,  vaseline,  paraffin,  etc. 

The  flashing  point  is  the  temperature  at  which  a  mixture  of  the 
vapor  of  kerosene'  and  air  can  be  set  on  fire. 

Dry  distillation  of  soft  coal  gives  illuminating  gas,  ammonia,  coal 
tar,  coke,  etc.  Dry  distillation  of  wood  gives  wood  spirit,  acetic  acid, 
charcoal,  etc. 

Carbon  dioxide  is  formed  by  the  burning  of  carbon  and  its  com- 
pounds, by  the  breathing  of  animals,  by  the  action  of  acids  upon  car- 
bonates, by  fermentation,  by  the  action  of  baking  powders,  and  by  the 
heating  of  limestone. 


124  CARBON  AND  ITS  COMPOUNDS 

It  is  a  colorless  gas,  heavier  than  air,  somewhat  soluble;  it  neither 
burns  nor  permits  other  things  to  burn.  Carbon  dioxide  is  used  to 
raise  dough,  as  a  fire  extinguisher,  and  as  the  material  needed  to  harden 
plaster  and  mortar.  By  its  presence  in  water  it  causes  limestone  to 
dissolve.  It  serves  as  a  food  for  plants. 

Limestone  is  calcium  carbonate',  so  are  marble,  coral,  etc.  When 
limestone  is  heated  very  hot,  lime  remains.  Lime  and  water  combine 
to  give  "  slaked  lime,"  or  calcium  hydroxide.  Lime  water  is  a  solution 
of  calcium  hydroxide. 

134.  Exercises. 

1.  What  is  the  danger  of  sleeping  in  a  room  containing  a  stove? 

2.  When  soda  is  put  with  tomatoes,   effervescence  takes  place. 
What  gas  is  being  formed,  and  why? 

3.  How  could  you  remove  the  limestone  of  a  bone,  so  that  you 
could  tie  the  organic  matter,  which  remains,  in  a  knot?    How  could 
you  destroy  the  organic  matter,  and  leave  the  mineral  matter? 

4.  Would  a  carbon  dioxide  fire  extinguisher  be  better  for  fires  near 
the  floor  or  near  the  ceiling? 

5.  If  a  candle  is  put  into  an  old  well,  and  "goes  out,"  what  gas  is 
probably  present?    Is  it  safe  for  a  man  to  enter  such  a  well? 

6.  Mines  are  sometimes  filled  with  "fire  damp,"  and  sometimes 
with  "choke  damp."     What  gas  is  "choke  damp?" 

7.  Open  stoves  —  "salamanders" — containing  burning   charcoal 
are  often  placed  in  freshly  plastered  buildings.    How  do  they  help 
to  harden  plaster? 

8.  Where  do  clams,  oysters,  snails,  etc.,  get  the  limestone  out  of 
which  they  build  their  shells?    Where  does  the  limestone  of  our 
bones  come  from? 


FIG.  109. 

A  magnetized  needle  or 
bar  takes  a  N-S  position. 


CHAPTER  VIII 

MAGNETS  AND  ELECTRICITY 

135.  Magnets. —  It  was  known  to  ancient  peoples  that 
certain  specimens  of  iron  ore  could  draw  to  themselves 
bits  of  iron  or  steel.    These  specimens  came  to  be  called 
magnets,  from  Magnesia,  in  Asia  Minor, 

where  they  were  found.  Natural  mag- 
nets are  also  called  lodestones,  from 
"lode,"  a  vein  of 
iron.  When  a  lode- 
stone  is  suspended 
so  that  it  can  move 
freely,  it  points  north  and  south. 
If  a  bar  of  steel  is  rubbed  with  a  lode- 
stone,  it  becomes  magnetic  itself,  and 
likewise  points  north  and  south  when 
suspended  (Fig.  109) .  A  slender  mag- 
netized needle  or  bar  is  the  essential 
part  of  a  mariner's  compass.  The 
compass  was  known  before  the  days  of 
Columbus  (Fig.  110).  FlG.  m. 

Each  end  of  a   magnet 
attracts  iron  filings. 

136.  The  Poles  of  a  Magnet.— If  a 

magnetized  steel  knitting  needle  is  dipped  into  iron  filings, 
the  filings  are  attracted  by  the  needle  only  at  its  ends 
(Fig.  111).  If  the  needle  is  broken  in  two,  each  piece  is  a 

125 


FIG.  110. 

The  Thirty-two  "Points"  of 
a  Mariner's  Compass. 


126  MAGNETS  AND  ELECTRICITY 

magnet.  If  each  half  is  broken  in  two,  we  have  four 
magnets,  each  with  a  north-seeking  and  a  south-seeking 
end,  or  pole.  Finally,  if  we  lay  the  four  pieces  down  end 
to  end,  so  that  the  north-seeking  end  of  one  piece  touches 
the  south-seeking  end  of  the  next  piece,  all  the  four  pieces 
together  will  again  form  one  magnet,  which  will  attract 
iron  filings  only  at  the  two  ends. 
The  law  of  magnets  is : 

Like  poles  repel  each  other;  opposite  poles  attract. 

If  we  bring  the  north-seeking  end  of  a  bar  magnet  near 
the  south-seeking  pole  of  a  suspended  magnet,  they  will 
attract  each  other;  but  if  the  two  north- 
seeking  ends  are  brought  together, 
there  will  be  repulsion  between  them 
(Fig.  112). 

FIG.  112. 

137.  Magnetic  Substances.— A  mag- 
net of  steel  retains  its  magnetism  for  a 
long  while;  hence  it  is  called  a  permanent  magnet.    It 

will,   however,    lose   its    magnetism   if      s 

heated. 

If  one  pole  of  a  magnet  is  held  near  a 
piece  of  soft  iron,  such  as  a  nail,  the  nail  FlG  113> 

itself  becomes  a  magnet  (Fig.  113),  and    A0n^nhdel0df 
attracts  iron  filings  or  another  nail.   But      ^f  becomes  a  mag~ 
when  the  nail  is  removed  from  the  mag- 
net, its  magnetic  properties  disappear.     Thus,  while  steel 
can  be  permanently  magnetized,  soft  iron  forms  only  a 
temporary  magnet. 


THE  MAGNETIC  FIELD 


127 


It  is  not  necessary  for  the  magnet  to  touch  the  nail  in  order  that 
the  nail  may  become  a  magnet.  If  the  two  are  simply  brought  near 
each  other,  the  nail  takes  on  magnetic  qualities.  We  say  it  is  mag- 
netized by  induction.  Before  a  bit  of  iron  is  drawn  to  a  magnet,  it  is 
magnetized  by  induction,  and  its  N-seeking  pole  is  attracted  by  the 
S-seeking  pole  of  the  magnet,  while  its  S-seeking  pole  is  repelled  by  the 
S-seeking  pole  of  the  magnet. 

The  metals  cobalt  and  nickel  are  also  attracted  by  a  magnet,  but 
less  than  iron.  One  oxide  of  iron,  the  magnetic  oxide,  is  also  attracted, 
but  rust  is  not. 

138.  The  Magnetic  Field. —  That  a  magnet  can  affect 
a  magnetic  needle,  or  a  piece  of  nickel  or  iron,  without 
touching  it,  shows  that  a  magnet  affects  surrounding 
space;  that  it  has  about 
it  a  "  region  of  influence. " 
This  region  is  called  the 
magnetic  field  (Fig.  114). 
It  extends  in  all  direc- 
tions from  the  magnet, 
but  the  strength  of  mag- 
netic attraction,  like  that 
of  gravitation  (cf.  §  20), 
becomes  less  as  the  dis- 
tance from  the  magnet 

increases.  The  magnetic  needle  may  be  enclosed  in  glass, 
but  this  does  not  cut  off  the  magnetic  field.  Air  is  not 
necessary,  for  the  magnetic  influence  is  felt  in  a  vacuum. 

We  can  readily  trace  the  magnetic  field,  in  cross  section  (Fig.  114), 
by  placing  the  magnet  under  a  sheet  of  glass  or  cardboard,  and  sprin- 
kling iron  filings  upon  the  glass  or  cardboard  cover.  When  the  cover  is 
tapped  gently,  the  filings  arrange  themselves  end  to  end  in  the  magnetic 


FIG.  114. 

The  filings  arrange  themselves  parallel  with  the 
magnet's  "lines  of  force.  " 


128 


MAGNETS  AND  ELECTRICITY 


field.  If  we  use  a  cover  of  fresh  blue  print  paper,  and  expose  it  to 
light  with  the  filings  in  place,  the  position  of  the  filings  will  be  printed  on 
the  paper. 

139.  The  Earth  a  Magnet. —  The  earth  itself  is  a 
great  magnet,  having  its  north  and  south  poles.  It  is  to 
these  magnetic  poles,  not  to  the  geographical  poles,  that 

the  compass  needle 
points.  The  north  mag- 
netic pole  is  now  in 
Northern  Canada,  inside 
the  Arctic  Circle.  It  is 
slowly  moving  westward. 


30W 


FIG.  115. 

The  North  Magnetic  Pole,  the  "  Line  of  No  Vari- 
ation," and  the  "Declination"  in  Different 
Parts  of  North  America. 


The  latest  determination 
of  the  position  of  the  north 
magnetic  pole  was  made  by 
Amundsen,  the  Norwegian 
explorer,  in  1905;  he  found 
it  to  be  in  latitude  70°  5'  N., 
and  in  longitude  96°  46'  W. 
(Fig.  115).  This  is  the  same 
Amundsen  who  discovered 
the  earth's  south  geographical 
pole  in  1912. 


Since  the  earth's  north 
magnetic  pole  is  not  the  same  as  its  north  geographical 
pole,  a  compass  will  point  due  north  only  at  certain  places. 
The  "line  of  no  variation"  is  shown,  for  North  America, 
in  Fig.  115.  For  all  places  east  and  west  of  this  line  the 
compass  shows  a  variation,  or  declination,  from  true  north, 
and  the  amount  of  variation  must  be  known  if  the  com- 
pass is  to  be  used  accurately.  In  the  eastern  part  of  the 


EXERCISES  129 

United  States  and  Canada  the  compass  points  west  of 
north ;  in  the  western  part,  east  of  north. 

Columbus  knew  of  the  declination  of  the  needle,  and 
kept  a  record  of  its  amount  for  many  places  in  the  Atlantic ; 
but  to  his  sailors  it  was  a  source  of  great  uneasiness,  for 
they  thought  that  the  very  laws  of  nature  were  changed 
in  the  new  regions  they  passed  through  on 
their  long  voyage. 

Dipping  Needle. —  If  a  magnetized  needle  is  supported 
so  that  it  will  swing  in  a  vertical  plane  (Fig.  116),  instead 
of  horizontally,  it  is  called  a  dipping  needle.     Its  north- 
seeking  end  will  then  dip  noticeably  in  the  northern  hemi- 
sphere.   Over  the  north  magnetic  pole  it  will  stand  verti- 
cal, the  north-seeking  end  being  downward.    At  the  south 
magnetic  pole  the  north-seeking  end  of  the  compass  points 
upward.     It  is  plain  that  the  compass  cannot  tell  north  and  south 
directions  at  the  earth's  magnetic  poles,  because  there  the  magnetic 
force  is  all  vertical. 

140.  Exercises. 

l.-If  you  had  a  compass  and  a  bar  magnet,  how  could  you  tell, 
without  suspending  the  bar  magnet,  which  of  its  ends  was  north- 
seeking? 

2.  How  would  a  dipping  needle  behave  at  the  "magnetic  equator"; 
that  is,  on  a  line  half-way  between  the  earth's  magnetic  poles? 

3.  How  would  a  dipping  needle  behave  if  brought  near  a  large 
deposit  of  iron?    How  would  a  compass  behave? 

4.  We  believe  that  in  a  magnet  the  iron  molecules  are  themselves 
magnets,  set  end  to  end.    Draw  a  sketch  of  such  an  arrangement, 
marking  the  poles  of  each  small  magnet  N  and  S  respectively. 

5.  When  a  steel  bar  is  held  in  the  direction  taken  by  a  dipping 
needle,  that  is,  pointing  to  the  earth's  magnetic  pole,  sharp  blows  on 
one  end  of  the  bar  cause  it  to  become  a  magnet.  Suggest  the  reason. 


130  MAGNETS  AND  ELECTRICITY 

6.  How  could  ships  be  steered  in  the  right  direction,  out  of  sight  of 
land,  without  the  use  of  a  compass? 

7.  Why  are  some  magnets  made  in  horseshoe  form? 

141.  Electric  Charges  from  Friction. —  If  a  glass  rod  is 
rubbed  with  silk,  the  rod  will  attract  light  bodies,  such 
as  paper,  pith  balls,  cork,  etc.  (Fig.  117).  If 
a  pane  of  glass  is  placed  upon  two  books, 
and  rubbed  with  silk  (Fig.  118),  bits  of  paper 
or  cork  that  are  placed  under  the  glass  will 
be  set  in  motion.  A  stick  of  sealing  wax,  or 
a  hard-rubber  ruler  or  comb,  has  the  same 
power  after  it  has  been  rubbed  with  fur  or 
flannel  or  hair.  The  silk,  flannel,  and  hair 
FIG.  117.  become  electrified,  as  well 

The      charged  . ,  -,  11 

rod  first  at-     as  the  glass,  wax,  and  rub- 
tracts  and  *         ' 


ber.       In  fact,    any  two 
unlike    substances    are  FIG.  us. 

"charged"  by  rubbing;  a  part  of  the  ^JjJk^Lifetft 
muscular  energy  used  up  in  the  rub-     ^enath  move  up  and 
bing  is  changed  into  electric  charges. 

The  ancient  Greeks  knew  that  amber,  a  fossil  gum, 
would  attract  bodies  after  being  rubbed.  Amber  was  called 
"electron";  hence  our  words,  electric,  electricity,  etc. 

142.  Conductors  and  Insulators. —  Dr.  Gilbert,  the 
physician  of  Queen  Elizabeth,  found  that  some  bodies 
could  be  electrified  by  rubbing,  and  that  others  could  not. 
So  he  divided  bodies  into  "electrics"  and  "non -electrics." 
Because  metal  rods,  held  in  his  bare  hand  while  being 
rubbed,  were  not  charged,  he  called  metals  "non-electrics." 
If  he  had  held  the  metal  in  a  dry  wooden  or  silk  handle, 


ATTRACTION  AND  REPULSION 


131 


he  could  have  electrified  the  metal  as  well  as  the  glass. 
His  own  body  acted  as  a  conductor,  and  the  charge  passed 
through  it  to  the  earth.  We  now  call  bodies  conductors, 
or  non-conductors. 

Non-conductors  are  also  called  insulators,  from  the  Latin,  insula, 
an  island.  A  charge  formed  on  one  end  of  a  glass  rod  remains  where  it. 
was  produced;  but  if  one  end  of  a  metal  rod  is  rubbed,  the  whole  rod  is 
charged.  The  glass  is  an  insulator,  the  metal  a  conductor;  but  both 
are  "electrics."  Some  of  the  best  conductors  are:  metals,  charcoal, 
water  vapor,  and  wet  substances  generally.  Some  of  the  best  insula- 
tors are:  dry  cotton,  wool,  wood,  silk,  glass,  wax,  rubber,  and  shellac. 
Since  the  earth  is  a  good  conductor,  a  charged  conductor  will  lose  its 
charge  if  it  is  not  insulated  from  the  earth. 

143.  Attraction  and  Repulsion. —  If  an  electrified  body 
is  brought  near  bits  of  paper,  they  are  first  attracted,  and 
then  repelled.  This  phenomenon  is  studied 
most  easily  if  an  "electric  pendulum"  is 
used.  One  is  shown  in  Fig.  119.  It  is  sim- 
ply a  ball  of  pith,  or  of  cork,  suspended  by 
a  thread  which  insulates  it.  If  a  glass  rod, 
charged  by  rubbing  it  with  silk,  is  held  near 
the  ball,  the  ball  is  attracted  to  the  rod. 
After  it  has  obtained  a  charge  from  the  rod, 
it  is  repelled.  If  a  stick  of  sealing  wax, 
charged  by  rubbing  it  with  flannel,  is  now 
brought  near  the  charged  ball,  the  ball  is 
attracted.  .Since  the  charged  sealing  wax  attracts  what 
the  charged  glass  repels,  we  say  that  the  glass  and  wax 
are  oppositely  charged. 

If  we  call  the  charge  on  the  glass  positive  (+),  that  on  the  wax  is 
negative  ( — ).  It  will  be  found  that  the  silk  has  received  a  negative 


FIG.  119. 

Like  charges  repel 
each  other. 


132  MAGNETS  AND  ELECTRICITY 

charge  by  being  rubbed  with  glass,  while  the  flannel  rubbed  with  wax 
or  rubber  receives  a  positive  charge. 

The  laws  of  charged  bodies  are  like  those  of  magnets  (cf.  §  136)  : 

1.  Charged  bodies  attract  uncharged  bodies. 

2.  Bodies  having  unlike  charges  attract  each  other. 

3.  Bodies  having  like  charges  repel  each  other.    The  space  sur- 
rounding a  charged  body  is  called  an  " electric  field"  (cf.  §  138). 

144.  Induction  of  Charges. —  We  have  learned  (§  143) 
that  an  uncharged  body  is  charged  by  contact  with  a 
charged  body.     It  may  also  be  charged  by  induction, 
without  contact.     A  simple  apparatus  for  showing  this 
is  an  egg  shell  covered  with_tin  foil  (Fig.  120).    If  a  posi- 
tively (+)  charged  glass  rod  is  brought 
near  the  shell  without  touching  it,  the 
shell  will  be  electrified  by  induction.    An 
uncharged  cork  ball  will  be  attracted 
by  either  end  of  the  shell.    If  the  glass 
rod  is  removed,  the  charges  disappear. 
We  say  they  neutralize  each  other.  We 

FIG.  120.  can  charge  the  shell  permanently  if  we 

Eggtnd1u±ngedby       remove  one  of  the  charges  induced  by 

the  glass  rod.    To  do  this  we  hold  the 

rod  near  the  shell,  as  before,  and  then  touch  with  the 

finger  the  end  of  the  shell  farther  away  from  the  rod. 

The  repelled  positive  charge  passes  through  the  hand  and 

body  to  the  earth.     If  the  glass  rod  is  now  removed, 

the  shell  will  have  a  negative  ( — )  charge. 

145.  Electric  Discharge. —  If  the  finger  is  held  near  a 
charged  glass  rod,  sparks  pass  between  the  two.     The 
sparks  are  larger  if  the  finger  is  held  near  a  charged 


ELECTRICITY  OF  THE  ATMOSPHERE 


133 


conductor,  for  the  whole  conductor  is  discharged  at  once. 
The  strain  in  the  electric  field  is  greatest  around  the  points 
of  an  object;  hence  a  discharge  takes  place  very  easily 
from  points,  but  less  readily  from  blunt  portions.  When 
the  spark  passes,  the  air  is  heated,  and  its  rapid  expansion 
and  contraction  produce  a  sharp  explosion." 

146.  Storing  a  Charge;  the  Leyden  Jar. —  Apparatus 
for  storing  frictional  electricity  (Fig.  121)  is  made  of  two 
conductors  (metal  foil)  separated  by  a  non-conductor, 
such  as  glass.  If  one  conductor  is 
connected  with  a  source  of  positive 
charges,  while  the  other  conductor 
is  connected  with  the  earth,  the 
negative  charge  of  the  second  con- 
ductor is  held  on  the  side  of  the 

metal  next  to  the  glass,  but  the  positive 
charge  of  the  second  conductor  is  repelled 
to  the  earth.  If  the  earth  connection  is 
then  removed,  we  have  a  large  positive 
charge  on  one  side  of  the  glass,  and  a 
correspondingly  large  negative  charge 
on  the  other  side. 


Earth 


FIG.  121. 
An  Electric  Condenser. 


Ear 


FIG.  122. 

The  Leyden  Jar;  an 
Electric  Condenser 
and  Storing  Appa- 
ratus. 


The  most  common  form  of  the  apparatus  is 
the  Leyden  jar  (Fig.  122);  this  consists  of  a  glass 
bottle,  partly  covered,  both  inside  and  outside, 
with  metal  foil.  If  we  charge  the  j  ar  with  frictional 

electricity,  and  then  almost  connect  the  two  foils  by  some  conductor, 

a  strong  spark  discharge  takes  place. 

147.  Electricity  of  the  Atmosphere. —  Benjamin  Frank- 
lin showed  that  a  lightning  discharge  was  only  a  large 


134 


MAGNETS  AND  ELECTRICITY 


spark  of  electricity.  One  day  in  June,  1752,  when  a 
thunderstorm  was  coming  on,  he  sent  up  a  kite  having 
at  its  top  a  pointed  wire.  On  the  lower  part  of  the  string 
he  had  a  key,  and  the  kite-string  was  insulated  from  the 
earth  (Fig.  123). 

When  the  kite-string  became  wet,  so  that  it  could  con- 
duct electricity,  Franklin  obtained  sparks  from  it.    The 

sparks  were  ex- 
actly like  those 
obtained  by  fric- 
tion. 

When  two 
charged  clouds 
approach  each 
other,  the  strain 
in  the  "electric 
field"  between 
them  becomes  so 
great  that,  finally, 
the  charge  bursts 
through.  This  is 
lightning  (Fig. 
124).  If  the 
charge  passes  be- 
tween a  cloud  and 

the  earth,  we  say  that  the  lightning  strikes.  The  two 
clouds,  or  a  cloud  and  the  earth,  with  the  non-conduct- 
ing air  between  them,  thus  form  a  huge  Ley  den  jar. 

Thunder  is  due  to  the  rapid  expansion  and  contraction 
of  the  air  heated  by  the  lightning. 

148.  Lightning  Rods.—  The  electric  charge  " induced"  on  the  earth 


Insulator 


FIG.  123. 

Franklin's  kite  was  "charged  by  induction"  from  a 
charged  thundercloud.     Note  the  spark. 


EXERCISES 


135 


by  a  passing  thundercloud  is  greatest  in  projecting  objects,  such  as 
trees,  spires,  and  hilltops  (cf.  §  145).  Commonly  the  leaves  of  trees 
conduct  the  charge  from  the  earth  quietly,  as  a  "silent  discharge," 
and  prevent  the  striking  of  lightning.  Franklin  reasoned  that  a 
pointed  conductor — a  lightning  rod — would  perform  the  same  ser- 
vice for  a  house.  To  be  a  real  protection  a  lightning  rod  should  have  a 
large  diameter,  should  have  a  large  number  of  points,  and  should 
extend  far  enough 
into  the  ground  so 
that  it  will  always 
end  in  moist  earth. 

149.  Exercises. 

1.  When   hair    is 
combed  or  brushed 
vigorously   in    cold, 
dry  weather,  it  often 
' '  fluffs  out,"  showing 
that   the  individual 
hairs    are    repelling 
one     another.     Ex- 
plain. 

2.  If,     in    cold, 
dry     weather,     you 
' '  skate  "  in  your  slip- 
pers across  a  woolen 

carpet  or  rug,  and  then  bring  the  tip  of  your  finger  near  a  gas  jet  or 
other  metal  object,  a  spark  often  passes  between  your  finger  and  the 
object.  Explain  why. 

3.  If  you  rub  a  stick  of  sealing  wax  with  flannel,  the  wax  receives  a 
negative  ( — )  charge.     If  the  charged  wax  is  brought  near  an  un- 
charged "electric  pendulum,"  what  happens?    When  the  pendulum 
is  repelled,  what  kind  of  a  charge  does  it  have?     If,  now,  you  bring 
near  the  charged  pendulum  a  rubber  comb  which  has  been  rubbed 
with  flannel,  and  you  find  that  the  comb  repels  the  pendulum,  what 
kind  of  a  charge  is  there  on  the  comb? 


A  Lightning  Discharge. 


FIG.  124. 

Field  Museum  of  Natural  History. 


136 


MAGNETS  AND  ELECTRICITY 


4.  Why  is  it  dangerous  to  stand  under  a  tree  in  a  thunderstorm? 

5.  Read  about  the  life  of  Benjamin  Franklin.     What  did  he  do  for 
science,  for  business,  and  for  the  American  Colonies? 

150.  Electric  Currents. —  Magnetism  and  frictional 
electricity,  the  two  kinds  of  electrical  phenomena  already 
studied,  are  closely  related  to  the  third  form,  electric 
currents.  The  study  of  currents  begins  with  the  electric, 
or  "voltaic,"  cell,  a  contrivance  by  which  the  energy  set 
free  in  certain  chemical  reactions  appears  in  the  form  of 
electricity,  instead  of  as  heat  or  light  (cf.  §§  51,  105,  and 
109).  Methods  of  producing  currents  were  first  studied 
by  Galvani,  in  1786,  and  by  Volta,  in  1792. 

We  have  already  learned  (cf.  §  103)  that  zinc  and  dilute 
sulphuric  acid  give  hydrogen.  The  chemical  change  also 

produces  a  substance  called  zinc 
sulphate.  Besides  both  of  those  the 
reaction  produces  heat.  But  when 
both  zinc  and  copper  are  put  into 
dilute  sulphuric  acid  (Fig.  125), 
and  the  ends  of  the  metals  outside 
of  the  liquid  are  joined,  a  current 
flows  through  the  wire,  the  metals, 
and  the  liquid.  The  metals  may 
be  joined  by  simply  allowing  them  to  touch  each  other. 
The  zinc  wastes  away,  just  as  when  it  is  used  alone;  but 
in  exchange  we  get  the  current. 

A  simple  way  to  find  out  whether  or  not  a  current  is  passing  through 
the  wire  connecting  the  metals  is  to  " taste"  the  current.  We  do  this 
by  touching  the  tongue  with  the  ends  of  the  wires  a  little  distance 
apart.  The  current  produces  a  sharp  sensation. 


Copper 


Cop-  Zinc 
per 


FIG.  125. 

Two  Forms  of  the  Simple  Cell. 
The  current  flows  in  the  di- 
rection of  the  arrows. 


KINDS  OF  CELLS  137 

In  making  a  cell  we  may  use  other  metals  instead  of  zinc  and  copper. 
We  choose  one  metal  that  acts  readily  with  the  acid,  arid  one  that  does 
not.  Carbon  plates  are  often  used  instead  of  copper  ones.  Both 
plates  must  be  conductors.  Solutions  of  other  acids,  of  bases,  or  of 
certain  salts  (cf.  §§  214,  218,  and  220)  may  be  used  instead  of  the 
dilute  sulphuric  acid. 

To  bring  the  free  ends  of  the  metals  into  connection,  so  that  there 
can  be  a  current,  is  called  ''making,"  or  "closing,  the  circuit";  the  re- 
verse is  called  "breaking,"  or  "opening,  the  circuit"  (cf.  §  100).  A 
number  of  properly  connected  cells  is  called  a  battery. 

151.  Kinds  of  Cells. —  The  voltaic  cell  is  of  little  prac- 
tical use  in  its  simplest  form,  because  it  is  soon  weakened, 
or  stopped  entirely  (we  say  it  is  "  polarized "),  by  the 
bubbles  of  hydrogen  that  collect  upon  the  copper  plate. 
The  hydrogen  is  formed  by  the  action  between  the  zinc 
and  the  acid.  A  description  of  DanielFs  cell  —  also  called 
the  gravity  cell  —  will  show  one  way  in 
which  polarization  is  avoided. 

In  Darnell's  cell  (Fig.  126)  the  two  plates, 
zinc  and  copper,  are  given  a  "crowfoot" 
shape  to  increase  their  surfaces.     The  cop- 
per is  placed  at  the  bottom  of  the  jar  in  a 
saturated  solution  of  copper  sulphate  (blue 
vitriol),  while  the  zinc,  which  is  in  the  upper      A  Gravity,  or 
part  of  the  jar,  is  surrounded  by  dilute  sul-       Daniell>  G'eU* 
phuric  acid.    The  copper  sulphate  solution  is  the  heavier, 
and  remains  at  the  bottom;  hence  the  name ' t  gravity  "  cell. 

The  action  of  the  cell  is  as  follows:  The  zinc  reacts  with  the  dilute 
sulphuric  acid,  giving  zinc  sulphate  and  hydrogen.  The  hydrogen 
moves  toward  the  copper  plate;  but  in  passing  through  the  layer  of 
copper  sulphate  the  hydrogen  is  used  up,  and  copper  is  deposited  in  its 


138 


MAGNETS  AND  ELECTRICITY 


FIG.  127. 

Sal   Ammoniac    Liquid   and 
Dry  Cells. 


place.    Thus  polarization  is  prevented.     Daniell's  cell  is  much  used 
for  the  operating  of  telegraph  instruments  (cf.  §  155). 

152.  Sal  Ammoniac  Cells. —  Sal  ammoniac  cells  (Fig.   127)  are 
used  where  a  strong  current  is  needed  for  a  short  time,  as  for  ringing 

telephone  and  house  bells.  The  liquid  used 
is  a  water  solution  of  sal  ammoniac,  or  am- 
monium chloride  (cf.  §  112).  The  conduc- 
tors are  a  rod  of  zinc  and  a  plate  consisting 
of  carbon  and  manganese  dioxide. 

Dry  Cell.—  A  "dry"  cell  is  enclosed  in 
a  zinc  jar,  which  serves  as  the  zinc  plate. 
The  space  between  the  zinc  and  the  carbon 
is  filled  with  a  paste  consisting  of  sal  am- 
moniac, manganese  dioxide,  charcoal,  and  water.  The  cell  is  closed  so 
that  the  water  cannot  evaporate. 

153.  Currents   and   Magnetism. —  As   we   learned  in 
§  150,  we  can  test  a  circuit  for  the  presence  of  a  current 
by  bringing  the  free  ends  of  the  conducting  wires  in  con- 
tact with  the  tongue.    Of  course  this  will  not  do  for  very 
weak  or  very  strong  currents.    A  second  way  of  testing 
for  a  current  is  to  bring  the  wire  of  a  closed  circuit  near 
a  magnetic  needle  or  compass.    The  needle  will  be  turned 
from  its   N-S   position.     If   the  current  is  sufficiently 
strong,  and  the  bare  conducting  wire  is  dipped  into  iron 
filings,  some  of  the  filings  will  cling  to  the  wire. 

Both  of  the  last  two  tests  show  that  a  wire  carrying  a 
current  is  surrounded  by  a  magnetic  field:  that  it  is  a 
magnet. 

154.  Electromagnets. —  Since    a    conductor    that    is 
carrying  a  current  is  surrounded  by  a  magnetic  field,  we 


THE  TELEGRAPH 


139 


should  expect  that  a  piece  of  soft  iron  placed  inside  a  coil 
of  the  wire  would  become  a  temporary  magnet,  just  as 
when  it  is  in  the  field  of  a  bar  magnet  (cf.  §  137). 
Such  magnets  are  called  electromagnets.  The 
coil  must  be  made  of  insulated  wire,  so  that 
the  successive  turns  may  not  touch  one  an- 
other. If  they  do  touch,  the  current  will  not 
pass  through  all  the  wire,  but  will  be  "  short 
circuited. "  The  greater  the  number  of  turns  in 
the  coil  the  stronger  the  magnetic  field  will  be, 
and  the  stronger  the  electromagnet.  But  as 
soon  as  the  circuit  is  broken,  the  electromagnet 
is  demagnetized. 

The  coil  of  wire  is  called  the  helix;  the  iron  is  called 
the  core.  A  core  made  up  of  a  bundle  of  small  iron  wires 
makes  a  much  stronger  electromagnet  than  one  in  a  single 
piece.  Telegraph  instruments,  telephone  bells,  electric 

doorbells,  fire  alarms, 
and  many  other  de- 
vices are  operated  by 
electromagnets. 

Earth_  j_  _ 
FIG.  129. 


A  Simple  Telegraph  Instrument.  When  the  key  is 
pressed,  the  circuit  is  made  complete,  and  the  sound- 
er is  drawn  down  by  its  electromagnet. 


155.  The  Tele- 
graph. —  The  tele- 
graph instrument 
(Fig.  129)  consists  essentially  of  a'  key  for  making  and 
breaking  the  circuit  in  an  electromagnet,  and  thus  pro- 
ducing "clicks"  in  the  sounder.  The  sounder  is  a  small 
lever  (cf.  §  198)  which  is  held  by  a  spring  against  its  upper 
stop.  Opposite  the  core  of  the  electromagnet  is  a  piece  of 
soft  iron  called  the  armature.  When  the  key  is  pressed 


140  MAGNETS  AND  ELECTRICITY 

down,  and  the  circuit  is  thus  closed,  the  core  is  magnetized, 
and  draws  the  sounder  to  the  lower  stop.  This  produces 
a  "  click."  When  the  key  is  released,  the  sounder  springs 
back. 

The  current  is  usually  supplied  by  a  "  gravity"  battery.  Only  one 
wire  is  needed,  for  the  return  circuit  is  through  the  earth  (cf.  §  146). 
There  is  no  interference  between  these  earth  circuits,  in  spite  of  the 
large  number  of  messages  passing  at  the  same  time. 

In  the  original  telegraph,  as  made  by  Morse  in  1832,  a  moving  strip 
of  paper  was  placed  under  the  sounder.  If  the  circuit  was  kept  closed 
a  very  short  time,  a  dot  was  made  upon  the  paper;  if  for  a  longer  time, 
a  dash  was  the  result.  Combinations  of  dots  and  dashes  made  up  the 
alphabet.  The  "  printing  telegraph"  is  rarely  used  now,  for  messages 
are  taken  much  more  rapidly  by  ear. 

The  telegraph  code  is  as  follows: 


I    -  „  ----  2  --  --- 

m  —  —  w  --  •  —  3  ----  -- 

n   --  x   -  —  -  -  4  ----- 

o  -  -  y  -  -    -  -  5  ~ 

p   -----  z   ---     -  6  ...... 

q    ----  &  ---- 

r    -     --  ,    -  ---  8  ----- 

s    ---  ?    ------  9  ----  - 

t    -  .    ------  0  — 


156.  The  Electric  Bell.—  The  electric  bell  (Fig.  130) 
has  a  push-button  for  closing  the  circuit  and  thus  operat- 
ing the  electromagnet.  The  hammer  of  the  bell  and  the 
armature  are  attached  to  a  spring.  When  the  electro- 
magnet attracts  the  armature,  the  hammer  strikes  the 
bell.  But  at  the  same  instant  the  circuit  is  broken,  and 
the  spring  throws  the  armature  back  against  the  stop. 
The  circuit  is  thus  closed  once  more,  and  the  armature  is 
again  attracted.  In  this  way  the  hammer  is  made  to  give 
the  bell  a  rapid  succession  of  blows. 


ELECTRIC  FURNACES 


141 


157.  Changes  Produced  by  the  Current. —  The  difficulty 
which  a  current  meets  in  passing  through  a  conductor 
is  called  resistance.    Some  substances  are  much  better 
conductors  than  others.    Thus,  a  silver 

wire  is  a  better  conductor,  that  is,  has  a 
smaller  resistance,  than  a  platinum  wire 
of  the  same  diameter.  For  any  given  ma- 
terial, the  smaller  the  diameter  of  the  wire 
the  greater  the  resistance.  The  heating 
effect  of  German  silver  wire  of  high  resist- 
ance is  used  in  the  electric  heater,  electric 
pad,  electric  flat-iron,  and  electric  stove. 
In  passing  through  a  fine  wire  of  platinum 
or  carbon,  the  current  finds  so  much 
resistance  that  it  heats  the  wire 
white  hot,  forming  the  incandes- 
cent- electric  light.  If  carbon 
wire  is  used,  it  must  be  placed  in  a  bulb  free 
from  air,  or  the  carbon  will  burn  up  (c/.  §  51). 
The  "arc"  electric  light  (Fig.  131)  consists  of 
two  pencils  of  gas  carbon  (cf.  §  119)  placed  such 
a  distance  apart  that  there  is  great  resistance 
at  the  gap  between  them.  The  heat  produced 
changes  some  of  the  carbon  to  the  vapor  state, 
and  makes  the  vapor  white  hot.  The  temper- 
ature produced  is  about  3,800°  C. 

158.  Electric  Furnaces. —  An  electric  arc  furnace  (Fig. 
132)  is  an  arc  lamp  enclosed  in  a  box  made  of  high-melting 
materials,  such  as  fire  clay,  lime,  or  magnesia  (magnesium 
oxide;  cf.  §  48). 


142 


MAGNETS  AND  ELECTRICITY 


The  resistance  furnace  (Fig.  133)  has  two  poles  able  to  deliver  a 
powerful  current.  We  "close  the  circuit"  by  packing  between  the 
poles  the  materials  that  are  to  be  heated.  The  resistance  due  to 

the  materials  changes  the  energy 
of  the  current  into  heat.  In  the 
intense  heat  of  electric  furnaces 
man  has  been  able  to  turn  metals 
like  gold  and  platinum  into 
vapors,  and  to  prepare  many 
substances  of  great  commercial 
importance.  Among  these  are 

graphite  (cf.  §  119),  carborundum,  a  very  hard  abrasive  (scouring 
and  polishing  material),  and  calcium  carbide,  a  gray  solid  that  reacts 
with  water  to  give  acetylene,  the  gas  used  in  acetylene  lamps  (cf. 
§257). 


FIG.  132. 
Electric  Arc  Furnace. 


159.  Electroplating. —  We  have  learned  that  when  the 
electric  current  is  passed  through  dilute  sulphuric  acid, 
hydrogen  collects  at  one  pole,  and  oxygen  at  the  other 
(cf.  §  100).  If  the  current 
is  passed  through  a  solu- 
tion of  copper  sulphate, 
copper  is  formed  at  one 
pole,  and  oxygen  and  sul- 
phuric acid  at  the  other.  FIG  133 

In     this     Case     the     COpper      Resistance    Furnace.      The  materials  to  be 

sulphate  is  used  up.  But 
if  the  pole  at  which  the 
current  enters  the  solution  is  of  copper,  the  copper  sul- 
phate is  not  used  up.  What  happens  is  that  copper  wastes 
away  at  one  pole,  and  is  deposited  at  the  other.  An 
object  placed  at  the  receiving  pole  will  be  electroplated 
with  copper. 


. 

heated  are  poured  through  the  hoppers 
A,  A,  and  the  current  is  passed  between 
B  and  B. 


DYNAMO 


143 


Battery 


FIG.  134. 

The  copper  plate  forming  the  +  electrode  (pole) 
wears  away,  but  an  equal  amount  of  copper  is  de- 
posited on  the  impression  of  the  type  (the  —  elec- 
trode). In  this  way  a  copper  film  is  formed  which 
is  the  exact  image  of  the  type. 


This  is  the  way  in  which  electrotype  plates  of  the  pages  of  books  are 
made  (Fig.  134).  An  impression  of  the  type  is  prepared  in  wax,  this  is 
covered  with  graphite  (cf.  §  119)  to  make  it  a  conductor,  and  the  wax 
mould  is  then  made  the 
receiving  pole  in  a  cop- 
per sulphate  "electrolytic 
bath."  The  copper  de- 
posit is  an  exact  copy  of 
the  type.  It  is,  however, 
very  thin;  hence  it  is 
strengthened,  at  the  back, 
by  a  filling  of  melted 
metal.  The  original  type 
is  free  to  be  used  over  and 
over  again  in  the  setting 
up  of  other  pages  of  the 
book. 

Silver-plating  (Fig.  135)  is  carried  out  in  a  similar  way.  The  solu- 
tion contains  a  silver  compound,  the  pole  that  wastes  away  is  of  silver,, 
and  the  object  to  be  plated  is  made  the  receiving  pole. 

160.  Dynamo. —  On  a  small  scale,  currents  may  be 
produced  by  batteries  (cf.  §  150) ;  but  for  larger  uses  men 
need  more  economical  and  more  powerful  generators. 

These  are  commonly  known 
as  dynamos. 

We  have  learned  that  when 
a  bar  of  soft  iron,  or  a  bun- 
dle of  soft-iron  wires,  is  put 
into  the  field  of  a  coil  carry- 
ing a  current,  the  soft  iron 

becomes  magnetized  (cf.  §  154) .  Equally  important  is  the 
fact  that  when  a  magnet  is  introduced  into,  or  removed 
from,  a  coil  of  insulated  wire,  a  current  is  produced 


Fia.  135. 
Silver-plating. 


144 


MAGNETS  AND  ELECTRICITY 


in  the  wire, 
kept  moving. 


The  current  flows  as  long  as  the  magnet  is 
This  is  illustrated  by  Fig.  136.  The  moving 
of  the  magnet  causes  the  wire 
constantly  to  pass  through 
new  portions  of  the  magnet's 
field. 

Instead  of  moving  the 
magnet  within  a  fixed  coil, 
we  can  keep  the  coil  in  mo- 
tion, while  we  leave  the 
magnet  stationary.  This  is  the  principle  of  the  dynamo 
(Fig.  137).  A  revolving  frame,  called  the  armature,  is 
wound  with  many  separate  coils  of  wire.  As  each  coil  ap- 
proaches and  leaves  the  magnetic  field,  currents  are  pro- 
duced in  the  wires.  These  are  drawn  off,  as  rapidly  as  they 


FIG.  136. 

A  magnet  moved  into  or  out  of   a  coil 
produces  a  current  in  the  coil. 


FIG.  137. 

A  Direct  Current  Dynamo,  Directly  Connected  with  an  Automatic  Engine.    Courtesy 
of  the  Ridgway  (Pa.)  Dynamo  and  Engine  Co. 

are  produced,  through  wires  attached  to  the  poles  of  the 
dynamo.  The  dynamo  current  may  be  used  for  the  pro- 
duction of  heat  or  light,  or  it  may  be  run  into  the  motors 
of  trolley  cars,  etc.,  and  used  to  produce  motion. 


ELECTRIC  POWER  145 

161.  Electric  Motors. —  The  motor  has  practically  the 
same  construction  as  the  dynamo,  but  its  action  is  that 
of  the  dynamo  reversed.     That  is  to  say,  while  in  the 
dynamo  we  cause  the  coils  of  the  armature  to  revolve  in 
the  field  of  the  magnet,  and  thus  produce  a  current,  in 
the  motor  we  run  a  current  into  the  armature,  and  cause 
it  to  revolve,  producing  motion.    The  motion  of  the  arma- 
ture can  be  passed  on,  by  gear  wheels  or  by  belts,  to  the 
wheels  of  a  street  car,  or  of  whatever  is  to  be  set  in  mo- 
tion.   In  other  words,  in  the  dynamo  we  exchange  mechan- 
ical motion  for  an  electric  current;  but  in  the  motor  we 
exchange  the  current  for  mechanical  motion. 

Electric  motors  are  used  not  only  for  the  moving  of  vehicles,  but 
also  for  running  the  machinery  of  factories,  sewing  machines,  washing 
machines  (cf.  Fig.  194), 
electric  fans,  vacuum 
cleaners,  etc.  e 

Electric  Street  Cars.— 
In  the  trolley  car  the 
motor  is  generally  under 
the  car,  and  the  current  is 

supplied  by  the  generators  (dynamos)  of  a  power  house  (Fig.  138). 
The  current  is  carried  by  a  "feed  wire"  to  the  trolley  wire,  or  third 
rail,  from  which  it  passes  to  the  motor  of  the  car.  The  return  circuit 
for  the  current  is  through  the  car  track. 

162.  Electric  Power. —  Electric  power  may  be  generated 
in  dynamos  by  engines  using  coal,  gasoline,  petroleum, 
etc.,  as  sources  of  energy,  or  the  power  may  come  from  the 
wind,  waterfalls,  rapids,  or  dams.    Niagara  furnishes  power 
not  only  for  many  electric  furnaces  and  for  processes  of 
electrolysis,  but  for  lighting  cities  like  Buffalo  and  Roches- 


146 


MAGNETS  AND  ELECTRICITY 


ter,  and  for  propelling,  lighting,  and  heating  trolley  cars 
within  a  considerable  distance.  The  control  of  water 
power  is  everywhere  giving  the  energy  needed  for  electric 
power  (Fig.  139).  This  is  true  of  the  great  dam  at  As- 
souan, in  Egypt,  the  Gatun 
dam  of  the  Panama  Canal, 
and  the  dam  across  the 
Mississippi,  at  Keokuk, 
Iowa  (Fig.  140). 


163.  Summary. —  Magnets 
are  natural  or  artificial.  Natural 
magnets  are  lodestones.  All 
magnets,  when  freely  suspen- 
ded, point  toward  the  earth's 
magnetic  poles,  unless  they  are 
interfered  with  by  large  masses 
of  iron,  or  by  local  magnetic 
fields. 

Two  magnetic  poles  of  the 
same  kind  repel  each  other; 
those  of  opposite  kind  attract 
each  other. 

Soft  iron  forms  temporary 
magnets;  steel  forms  permanent 
magnets.  Iron,  steel,  magnetic 
cobalt,  nickel,  etc.,  are  magnetic;  that  is,  attracted  by 


FIG.  139. 

Water  from  a  higher  level  falls  through  a 
penstock  against  the  guides  of  the  turbine. 
The  guides  direct  the  rushing  water  upon 
the  blades,  causing  them  to  revolve  rapidly. 
The  whirling  turbine  turns  the  shaft  and  the 
generator  attached  to  it. 


iron  oxide, 
a  magnet. 

A  magnet  attracts  a  magnetic  body  by  first  inducing  it  to  become  a 
magnet. 

The  earth  is  a  magnet,  with  two  magnetic  poles.    These  are  found 
by  the  dipping  needle,  as  well  as  by  the  compass. 

The  compass  has  been  of  the  greatest  use  in  the  development  of 
navigation  and  civilization. 

Frictional  electricity  is  commonly  developed  by  rubbing  two  sub- 


SUMMARY  147 

stances  together.  Conductors  can  be  electrified  only  if  held  by  means 
of  an  insulator. 

An  electrified  body  attracts  one  not  electrified,  then  charges  it  with 
its  own  kind  of  electric  charge,  and  then  repels  it. 

The  space  around  a  charged  body  is  an  electric  field.  An  insulated 
body  brought  into  the  field  is  electrified  by  induction. 


FIG.  140. 

Generator  Room  of  the  Mississippi  River  Power  Co.  at  Keokuk.  A  dam  4,649  feet  long 
extends  across  the  river,  and  raises  the  water  behind  the  dam.  Some  of  the  water 
rushes  through  turbines,  generating  200,000  horse  power  (cf.  §  26)  of  electricity. 
About  a  third  of  this  is  carried  to  St.  Louis,  137  miles  away. 

When  the  strain  in  the  electric  field  between  two  oppositely  charged 
bodies  becomes  sufficiently  great,  a  discharge  takes  place,  usually  as 
a  spark.  Discharge  takes  place  most  easily  from  points. 

An  electric  condenser  consists  of  two  conductors,  such  ^s  metal 
foil,  separated  by  a  non-conductor,  such  as  glass.  The  common  form 
is  the  Leyden  jar. 

Franklin  proved  that  lightning  is  a  huge  electric  spark.  His  kite  was 
electrified  by  induction  from  the  charged  cloud. 

Electric  currents  are  usually  generated  in  cells  or  by  dynamos. 

The  simple  cell  consists  of  zinc,  copper  (or  carbon),  and  dilute 
sulphuric  acid.  The  current  flows  from  zinc  to  copper  inside  the 


148  MAGNETS  AND  ELECTRICITY 

liquid,  and  from  copper  to  zinc  outside  of  the  liquid.  A  group  of  con- 
nected cells  is  a  battery. 

The  simple  cell  is  easily  polarized  by  the  hydrogen  which  collects 
upon  the  copper  (or  carbon)  plate.  Polarization  is  prevented,  in 
Daniell's  cell,  by  a  layer  of  copper  sulphate  solution  between  the  zinc 
and  the  copper.  In  other  cells  oxidizing  materials  are  put  into  the 
solution,  or  mixed  with  the  carbon.  These  convert  the  hydrogen  into 
water. 

Wires  carrying  currents  are  magnets.  Electromagnets  are  formed 
when  soft  iron  is  put  into  coils  carrying  currents. 

The  telegraph  is  essentially  an  electromagnet,  with  a  key  for  making 
and  breaking  the  circuit. 

The  electric  bell  is  an  electromagnet  in  which  the  armature  carrying 
the  hammer  continually  breaks  the  circuit,  causing  the  hammer  to 
vibrate  back  and  forth. 

The  resistance  which  the  current  meets  in  passing  through  con- 
ductors appears  as  heat.  This  is  the  principle  of  electric  lighting  and 
heating  devices. 

Electroplating  is  due  to  the  electrolysis  of  solutions  of  the  com- 
pounds of  certain  metals,  such  as  copper,  silver,  gold,  nickel,  etc. 

A  dynamo  is  a  device  in  which  coils  of  wire,  moving  rapidly  through 
the  fields  of  powerful  magnets,  produce  a  current. 

A  motor  is  a  dynamo  reversed.  In  it  an  electric  current  is  changed 
into  mechanical  motion. 

Men  get  electric  power  on  an  enormous  scale  by  changing  the 
mechanical  energy  of  falling  water  into  electric  currents. 

164.  Exercises. 

1.  If  »  piece  of  steel  is  held  near  a  dynamo,  it  is  pulled  strongly 
toward  the  dynamo.     If  held  there  for  a  short  time,  it  becomes  a 
magnet.    Explain  both  facts. 

2.  Write  in  the  Morse  code:    Will  visit  your  school  Tuesday, 
April  9.     Leave  short  spaces  between  letters  and  longer  ones  between 
words. 

3.  Read  an  account  of  the  life  of  Morse,  the  inventor  of  the  tele- 
graph. 


EXERCISES  149 

4.  What  is  meant  by  the  terms  "  triple  plate,  quadruple  plate," 
etc.,  as  applied  to  silver  utensils? 

5.  How  could  a  slab  of  impure  copper  be  purified  by  the  electric 
current? 

6.  How  could  coal  be  converted  into  energy  at  the  mine,  and  this 
energy  distributed  without  the  shipping  of  the  coal? 

7.  When  the  lighting  system  of  a  trolley  car  is  on  the  same  circuit 
as  the  power,  the  lights  often  burn  low  while  the  car  is  being  started, 
but  burn  brightly  when  the  car  is  in  motion.    What  does  this  show  as 
to  the  power  required  to  start  the  car  as  compared  with  that  needed  to 
keep  it  moving? 

8.  What  advantages  has  electric  power  over  steam  power  for  factory 
use?    For  the  home? 


CHAPTER  IX 

LIGHT  AND  SOUND 

165.  Luminous  Bodies. —  Every  object  that  we  see 
"  is  seen/'  or  "  is  visible/ '  because  light  from  the  object 
enters  the  eye.    When  the  visible  body  itself  produces  the 
light,  the  body  is  said  to  be  self-luminous.    Self-luminous 
bodies  are  usually  very  hot.    This  is  the  case  with  the  sun, 
a  lamp  flame,   an  arc   electric  light.     However,   most 
visible  bodies  are  not  self-luminous;  but  they  shine,  or  are 
seen,  by  light  which  they  receive,  and  then  reflect  to  the 
eye.     We  say  that  non-luminous  bodies  are  illuminated 
by  luminous  bodies.    The  moon  is  a  non-luminous  body. 
Moonshine  is  sunshine  reflected  to  us  from  the  moon's 
surface.     An  object  seen  by  moonlight  is  thus  seen  by 
sunlight  that  has  been  reflected  twice:    first  from  the 
moon  to  the  object,  and  then  from  the  object  to  the  eye. 
When  we  take  a  lamp  into  a  dark  room,  we  see  the  objects 
in  the  room,  because  they  reflect  lamplight  to  the  eye. 

166.  Transparent   and    Opaque    Bodies. —  Substances 
through  which  objects  are  seen  clearly  are  said  to  be 
transparent.    Such  are  water,  glass,  and  air.    A  substance 
that  does  not  permit  light  to  pass  through  it  is  said  to  be 
opaque.    Wood  and  iron  are  opaque.    Certain  substances 
allow  some  of  the  light  to  pass,  but  objects  cannot  be  seen 
distinctly  through  them;  such  substances  are  said  to  be 

150 


IMAGES   THROUGH  SMALL  OPENINGS  151 

translucent.  Examples  of  translucent  substances  are 
fog,  ground  glass,  oiled  paper,  and  thin  china.  Very  thin 
plates  of  all  bodies,  even  metals,  are  translucent.  Thus, 
gold  foil  transmits  a  green  light. 

167.  Light  and  Its  Properties. —  Light  is  the  cause 
outside  of  us  that  produces  the  sensation  of  sight.    Sun- 
light produces  other  effects  besides  the  lighting  of  objects. 
Thus,  if  the  skin  is  exposed  to  sunlight,  it  is  not  only 
illuminated,   but  also  warmed.     In  addition,   chemical 
changes  are  brought  about  in  the  skin,  and  it  is  tanned. 
The  energy  of  the  sun  thus  appears  as  heat,  light,  and 
chemical  energy. 

The  velocity  of  light  is  very  great:  about  186,000  miles  a  second 
(cf.  §  11).  Sound  waves  travel  through  air  at  the  rate  of  about  1,100 
feet  a  second;  but  this  is  a  snail's  pace  as  compared  with  light.  Be- 
cause of  the  greater  speed  of  light  we  see  the  flash  of  a  gun  before  we 
hear  its  report,  and  we  see  the  lightning  long  before  we  hear  the  thunder 
that  accompanies  it. 

Light  travels  in  straight  lines  through  a  transparent  substance,  if  the 
density  of  the  substance  is  the  same  throughout.  A  single  line  of  light 
is  called  a  ray,  and  a  number  of  parallel  rays  make  up  a  beam.  A 
sunbeam  is  an  example.  If  a  sunbeam  enters  a  dark,  dusty  room,  its 
straight  path  is  shown  by  the  illuminated  dust  particles.  On  a  foggy 
night  a  street  lamp  sends  out  straight  lines  of  light  in  all  directions. 
These  observations  show  that  light  travels  in  straight  lines.  The  same 
thing  is  shown  by  the  formation  of  images  and  shadows. 

168.  Images  Through  Small  Openings. —  An  easy  way 
to  learn  how  images  are  formed  is  to  let  light  pass  through 
the  small  opening  of  a  "  pin-hole  camera."    The  camera 
(Fig.  141)  consists  of  a  box  with  both  ends  removed.    A 
hole  is  cut  in  one  of  the  remaining  four  sides  of  the  box, 


152  LIGHT  AND  SOUND 

and  over  this  is  pasted  a  strip  of  tin  foil.  A  smooth  pin- 
hole  is  made  in  the  foil.  The  inside  of  the  box  is  black, 
except  for  a  white  space  just  opposite 
,-:-_-n  the  tin  foil.  If  the  room  is  darkened, 
-  Jw>  and  a  small,  lighted  candle  is  placed 
FIG  141  before  the  pin-hole,  an  image  of  the 

when  light  from  an  object  candle  is  seen  inside  the  box,  on  the 

passes  through  a   pin-hole 

into  a  darkened  box,  the  white  screen:  but  the  image  is  corn- 
image  is  inverted.  ' 

pletely  turned  about. 

The  explanation  is  as  follows: — The  candle  flame  is  sending  out 
rays  of  light  from  a  large  number  of  points  on  its  surface.  Each 
of  these  points  sends  a  small  beam  through  the  pin-hole,  and 
the  beam,  when  it  strikes  the  white  screen,  makes  an  image  of 
the  part  of  the  candle  flame  from  which  it  came.  But  all  the  beams 
cross  at  the  pin-hole.  Hence  the  light  from  the  top  of  the  flame  will 
form  the  bottom  of  the  image,  and  the  light  from  the  right  side  will 
form  the  left  side  of  the  image,  and  the  image  is  completely  inverted. 
A  landscape  seen  through  a  very  small  point  is  also  turned  about. 

169.  Shadows. —  That  light  travels  in  straight  lines  is 
shown,  also,  by  the  forming  of  shadows.  When  an  opaque 
body  is  put  in  the  way  of  light  rays,  it  cuts  off  the  light 
from  the  space  behind  it,  producing  a  shadow.  If  the 
source  of  light  is  very  small 
(S,  Fig.  142),  the  shadow  is 
very  distinct.  But  if  the 
luminous  body  has  a  consider- 
able surface,  and  sends  out  n  FIG.  142. 

The  shadow  cast  by  an  object  that  is 

light  from  many  points,  the     jJ^j^^arkSess  point  °f  light  is  °f 
shadow  will  have  two  parts: 

one  receiving  no  light  at  all,  and  the  other  getting  light 
from  part  of  the  luminous  surface,  but  not  from  all  of  it. 


BRIGHTNESS,   OR  INTENSITY,   OF  LIGHT 


153 


We  call  the  distinct  shadow,  which  receives  no  light  at  all, 
the  umbra;  the  indistinct  part  surrounding  the  umbra  is 
called  the  penumbra. 
Fig.  143  gives  the 
illustration : — 


FIG.  143. 

The  shadow  cast  by  an  object  that  is  illuminated  by 
the  sun's  surface  consists  of  umbra  and  penumbra. 


Let    us    suppose   that 
the   moon,  in  the   cone- 

«hnr»Prl   crmpp  to  tV»P  rio-Vit 
rigm 

of  the  earth,  is  entirely 
cut  off  from  sunlight.  To  an  observer  on  that  side  of  the  earth  the 
moon  would  be  entirely  eclipsed  by  the  earth's  shadow  (cf.  §  3).  To 
an  observer  on  the  moon  the  sun  would  be  entirely  eclipsed  by  the 
earth.  But  if  the  moon  were  in  the  penumbra  of  the  earth's  shadow, 
an  observer  on  the  moon  would  see  the  earth  as  a  black  body  covering 
part  of  the  sun's  disc,  but  not  all.  If  an  observer  could  stand  just  at 
the  tip  of  the  umbra,  and  facing  the  earth,  the  sun's  face  would  be  just 
exactly  covered  by  the  earth. 


170.  Brightness,  or  Intensity,  of  Light. —  We  all  know 
that  the  distance  of  an  object  from  a  source  of  light  affects 
the  amount  of  light  received  by  the  object,  or  the  intensity 
of  the  light.  Now,  if  one  boy  holds  his  book  twice  as  far 
away  from  a  reading  lamp  as  another  boy  does,  he  receives, 
not  %  as  much  light,  but  M  as  much  light  as  the  other. 
A  third  boy,  sitting  three  times  as  far  away  as  the  first, 
receives  only  l/9  as  much  light,  and  so  on. 

The  reason  for  this  is  shown  by  Fig. 
144.     Two  square  cards,  1  inch  and  2 
inches  on  each  edge,  respectively,  are 
placed  in  vertical  positions  on  the  same 
PIG  144  —    side  of  the  lamp.    The  lamp  should  be 

An  object  twice  as  far  from  the  lamp    Very  Small,  SO  that  its  light  shall  COHie 
as  another  gets  only  M  as  <•  ,  •      n  •    A.    /    /•     e    i  nr\\ 

much  light.  from  practically  one  point  (cf.  §  169). 


154 


LIGHT  AND  SOUND 


The  area  of  the  smaller  card  will  be  1  square  inch;  of  the  larger,  4 
square  inches.  If  we  place  the  smaller  card  4  inches  from  the  lamp, 
and  the  larger  card  8  inches  (twice  as  far)  from  the  lamp,  then  the 
shadow  cast  by  the  first  card  will  just  cover  the  second  card.  This 
means  that  the  light  which  falls  on  1  square  inch  at  distance  1  is 
spread  out  over  4  square  inches  at  distance  2.  Therefore  the  intensity, 
or  brightness,  of  the  light  on  the  more  distant  card  is  not  H  of  the 
brightness  on  the  nearer  card,  but  H  X  H,  or  3^  as  great. 

171.  Candle  Power. —  The  intensity  of  the  light  given 
off  by  lamps  is  always  stated  as  so  many  "  candle  power." 
This  is  because  the  unit  of  intensity  is  the  illuminating 
power  of  a  standard  candle.    The  standard  candle  is  of 
sperm  fat,  weighs  Ye  of  a  pound,  and  burns  at  the  rate  of 
120  grains  (7.78  grams)  an  hour. 

We  get  the  candle  power  of  a  lamp 
by  using  a  photometer  (Fig.  145).  This 
consists  of  a  piece  of  oiled  paper  or 
cardboard,  supported  in  a  frame,  and  a 
pencil  that  can  be  set  upright  near  the 
frame.  The  work  must  be  done  in  a 
room  that  is  dark,  except  for  the  lamp 
and  candle  to  be  compared.  These  two 
are  lighted,  and  placed  so  that  the  two 
shadows  of  the  pencil  shall  fall  on  the  oiled  screen  side  by  side.  The 
distance  of  the  lamp  or  candle  is  then  altered,  so  that  the  shadows  are 
equally  dark.  Suppose  that  the  distance  between  the  candle  and  its 
shadow  is  1  foot,  and  that  between  the  lamp  and  its  shadow,  4  feet. 
We  square  each  of  these  numbers;  that  is,  we  multiply  each  by  itself. 
The  square  of  1  is  1,  and  that  of  4  is  16.  So  the  lamp  has  an  illuminat- 
ing power  16  times  as  great  as  that  of  the  candle.  We  say  it  is  a  "  16 
candle-power  "  lamp. 

172.  Exercises. 

1.  At  about  525°  C.  iron  becomes  red  hot.     Is  iron  illuminated 


FIG.  145. 

How  to  get  the  "candle  power"  of 
an  electric  light. 


DIVISION  OF  THE  LIGHT  STRIKING  A  BODY        155 

or  self-luminous  when  we  see  it  below  this  temperature?    When  we  see 
it  above  this  temperature? 

2.  What  reasons  have  we  for  believing  that  the  moon  is  not  self- 
luminous? 

3.  Classify  the  following  substances  as  transparent,  translucent,  or 
opaque:  ice,  snow,  alcohol,  milk,  iron,  the  material  of  our  finger  nails, 
skin,  tissue  paper,  carbon  dioxide,  a  solution  of  blue  vitriol. 

4.  I  see  a  carpenter,  down  the  street,  driving  nails;  but  the  sound  of 
each  blow  comes  to  me  just  as  I  see  the  hammer  raised  for  the  next  blow. 
Why? 

5.  A  flash  of  lightning  is  seen  10  seconds  before  the  thunder  is  heard. 
How  far  away  is  the  thunder  cloud? 

6.  Sirius,  the  brightest  of  the  fixed  stars,  is  about  8  light-years 
distant  (c/§  11).    How  many  miles  is  this,  if  we  call  the  speed  of  light 
200,000  miles  a  second? 

7.  What  are  the  positions  of  the  sun,  the  moon,  and  the  earth  when 
we  have  "  new  moon  "?    When  we  have  "  full  moon  "?    At  which  of 
these  times  may  we  have  an  eclipse  of  the  moon?    At  which  an  eclipse 
of  the  sun? 

8.  Why  is  the  shadow  cast  by  a  light  of  small  diameter,  such  as  an 
electric  bulb,  so  distinct? 

9.  I  sit  5  feet  from  a  lamp,  while  my  brother  is  1  foot  from  the 
lamp.    How  much  more  light  does  he  get  than  I? 

10.  In  a  photometer  (Fig.  145)  a  candle  at  a  distance  of  1  foot  casts 
a  shadow  just  as  dark  as  one  cast  by  a  lamp  6  feet  away.    What  is  the 
lamp's  candle  power? 

173.  Division  of  the  Light   Striking   a  Body. — When 
light  meets  a  body,  several  things  may  happen : — 

(1)  The  light  may  be  thrown  back  —  reflected  —  in 
a  regular  way  and  in  certain  definite  directions. 

(2)  It  may  be  reflected  irregularly  —  dispersed — in 
all  directions. 

(3)  It  may  pass  through  the  body  it  meets. 

(4)  It  may  be  absorbed  by  the  body. 


156 


LIGHT  AND  SOUND 


FIG.  146. 

The  angle  of  incidence  is  equal  to  the  angle  of 
reflection. 


Usually  two  or  more  of  these  results  take  place  at  the 
same  time. 

174.  Reflection  of  Light. —  If  you  throw  an  elastic 
ball,  such  as  a  tennis  or  golf  ball,  vertically  downward 
against  a  horizontal  sidewalk,  you  expect  it  to  bound  back 
vertically  upward.    But  if  you  throw  the  ball  downward  in 
an  inclined  direction,  as  A  C  of  Fig.  146,  it  bounds  off  in 

another  inclined  direc- 
tion CB.  Except  for  the 
effect  of  gravity  on  the 
ball  (cf.  §  21)  the  angle 
made  by  AC  with  CD 
(angle  A  CD)  is  of  the 
same  size  as  the  angle 
made  by  CB  with  CD 
(angle  BCD).  The  first  angle  (A  CD)  is  called  the  angle 
of  incidence  (i.  e.,  falling  upon);  BCD  is  the  angle  of 
reflection  (i.e.,  bending  back).  The  rule  is: — 
The  angle  of  incidence  equals  the  angle  of  reflection. 
Light  and  sound  are  reflected  in  the  same  way  as  the 
ball.  If  A  of  Fig.  146  represents  a  small  opening  through 
which  a  beam  of  light  is  admitted  into  a  dark  room,  and 
if  the  reflecting  surface  at  C  is  a  smooth  plane  mirror,  you 
will  see  the  reflected  beam  only  when  your  eye  is  placed 
somewhere  on  the  line  CB. 

175.  Mirrors. — 'A  mirror,  or  looking-glass,  is  a  good 
reflector  of  light,  because  at  its  back  there  is  a  thin  layer 
of  a  metal,  usually  silver.    You  have  noticed  that  when  you 
look  at  any  object,  including  yourself,  in  a  mirror,  the  right- 
hand  side  of  the  object  becomes  the  left-hand  side  of  the 


MIRRORS 


157 


R 

FIG.  147. 


image  of  the  object.     If  an  open  book  is  held  toward  a 

mirror,  the  image  has  the  printed  matter  backward.    A 

watch  showing  9  A.  M.  forms  an  image  in  N 

which  the  hands  are  where  we  expect  ~ 

them  to  be  at  3  p.  M.     Let  us  see  how 

the  regular  reflection  of  light  produces 

images. 

Suppose  that   MR    of    Fig.    147    represents    a    The  eye  sees  an  object  in 

...  ,.  the  direction  from  which 

vertical  mirror,  and  that  a  point  or  some  object  the  light  of  the  object 
is  at  0.  Rays  of  light  from  0 
strike  the  surface  of  the  mirror  everywhere;  but  only 
the  ray  that  meets  the  mirror  at  F  passes  to  the  eye, 
according  to  the  rule  of  reflection  (§174).  But  the  eye 
sees  0  only  in  the  direction  from  which  the  light  ray 
comes  as  it  enters  the  eye;  so  0  appears  to  be  in  the 
imaginary  position  Of  (read  this:  0  prime).  0'  is  just  as 
far  back  of  the  mirror  as  0  is  in  front  of  it.  Now  suppose 
that  the  object  is  not  one  point,  but  many  points.  An 

The  image  of    arrow  is  a  convenient  form  of  object  (Fig.  148).     The 

fn°aJpCiaene    image  of  the  arrow  is  of  the  same  shape  as  the  arrow 

skuTup  "but    itself,  but  reversed  sidewise. 

Ibt^ieft       A  piece  of  polished  plate  glass  (Fig.  149),  if 
looked  at  at  the  right  angle,  will  be  a  mirror, 

and  yet  be  a  transparent  body  at  the 

same  time.     If  a  bottle  of  water  is 

placed  behind  the  glass,  and  a  burning 

candle  in  front  of  it,  we  see  both  objects 

in  the  direction  from  which  their  light 

comes  to  the  eye.    Hence  the  candle 

and  the  bottle  appear  to  be  in  the 

same  place,  behind  the  plate  glass,     Athickglasspiat9e  acts  both 

and  the  candle  seems  to  be  burning  in       transmitter^  fight  ;athl 

. -i  candle  seems  to  be  burn- 

tne  Water.  ing  in  the  water. 


FIG.  148. 


158  LIGHT  AND  SOUND 

176.  Diffused  Light.  —  When  a  reflecting  surface  is 
rough,  the  light  striking  it  is  dispersed  in  all  directions. 
It  is  by  diffused  light  that  we  see  most  objects.  Daylight 
is  sunlight  dispersed  by  reflection  from  the  ground,  trees, 
houses,  dust,  clouds,  etc.  Moonlight  is  uniformly  diffused 
sunlight  from  the  moon's  surface.  We  see  the  "  old  moon 
in  the  new  moon's  arms  "  by  earthshine; 
that  is,  by  sunlight  that  has  been  re- 
flected by  the  earth  to  the  moon,  and 
has  then  come  back  to  the  earth. 


FIG.  150.  177>  Refraction  of  Light.—  Let  us 

If  an  object  under  water  is  ^ 

looked  at  obliquely,  it  suppose  that  in  Fig.   150  we  have  a 

seems  to  be  at  one  side  of 


and    vessel  partly  filled  with  water,  and  that 
we  drop  a  stone  (S)  into  it.     To  the 
eye  the  stone  does  not  appear  to  be  S,  but  a  little  to  one 
side,  and  nearer  the  surface;  that  is,  at  S'. 

The  explanation  is  that  water  is  denser  than  air  (cf. 
§  33),  and  that  the  light  which  comes  from  the  stone  to  the 
eye  is  bent  at  B,  where  it  passes  from  water  into  air.  It 
is  bent  away  from  the  direction  of  the  line  SB.  Since  we 
see  an  object  in  the  direction  which  its  light  has  as  it 
enters  the  eye,  the  stone  appears  to  be  at  S'. 

Because  light  is  refracted  in  passing  from  water  into  air,  the  water 
of  a  pond  or  stream  seems  to  be  more  shallow 
than  it  really  is,  and  a  reed  or  an  oar  seems  to  be 
bent  where  it  enters  the  water.  For  a  similar  reason 
a  star  near  the  horizon  appears  to  be  higher  up 
than  it  really  is  (Fig.  151).  Its  light  is  bent  as 


it  enters  the  earth's  atmosphere   (cf.  §  38)  from  A  ^Jj^  hori. 

outside  space.    The  amount  of  bending  increases  as  zon  appears  to  be 

,,  higher    up    than    it 

the  star's  light  approaches  the  earth,  because  the  really  is. 


COMPOSITION  OF   WHITE  LIGHT 


159 


FIG.  152. 

Forms  of  lenses. 


air  becomes  more  and  more  dense  (cf.  §  41).  A  heavenly  body  is, 
therefore,  never  where  it  seems  to  be,  except  when  it  is  at  the  zenith; 
that  is,  directly  overhead. 

178.  The  Lens. — A  lens  is  a  piece  of  transparent  mate- 
rial, usually  glass,  having  two  curved  surfaces,  or  a  curved 
and  a  plane  surface.  Six 
forms  of  lenses  are  shown  in 
Fig.  152.  When  rays  of  light 
pass  through  a  lens,  they  are 
bent  toward  the  thickest  part 
of  the  lens.  This  is  shown  in 
Fig.  153.  Parallel  rays  coming  from  the  left  would  thus 
be  brought  together,  or  "  brought  to  a  focus/7  at  F,  on 
the  opposite  side  of  the  lens.  If,  on  the  other  hand,  light 
were  produced  at  the  point  F,  and  its  rays  went  through 

the  lens,  they  would  be  made  parallel. 

Focus  is   from  the   Latin,   and   means 

"  hearth." 

Burning  Glass.  —  The  double-convex  lens  of 

Fig.  153  would  bring  parallel  heat  rays,  as  well 

as  sunlight,  to  a  focus  at  F.  It  would  then  be 
called  a  "  burning  glass."  Paper,  or  a  match,  at  F  could  be  set  on 
fire. 

Refraction  of  Sound. — If  a  lens  were  constructed  of  the  right  mate- 
rial, it  could  refract  sound  waves  (cf.  §  190),  and  bring  them  to  a  focus. 
The  ticking  of  a  watch  might  then  be  heard  at  this  focus,  although  not 
at  places  much  nearer  the  watch  (Fig.  154). 


179.  Composition  of  White 
Light. —  At  first  thought  it  may 
seem  likely  that  white  light,  such 
as  that  of  the  sun,  is  simpler  in 


FIG.  153. 

The  lens  brings  the  par- 
allel rays  to  a  focus. 


FIG.  154. 

Sound  waves  can  be  brought  to 
a  focus  like  light  waves. 


160 


LIGHT  AND  SOUND 


Fia.  155. 

A  glass  prism  breaks  up  white  sunlight  into 
light  of  seven  well-marked  colors. 


its  composition  than  colored  light;  but  this  is  not  so.  If 
a  beam  of  sunlight  is  admitted  through  a  narrow  slit  (A) 
into  a  dark  room  (Fig.  155),  an  image  of  the  opening  will 
be  made  upon  the  screen  at  B.  But  if  a  glass  prism  (P) 
is  put  in  the  path  of  the  sunbeam,  the  image  of  the  slit 
will  not  be  a  simple  line,  but  a  series  of  lines  side  by  side; 
that  is  to  say,  a  band.  The  image  will  not  be  white,  but 
will  consist  of  bands  of  different  colors.  As  the  prism  is 

placed  in  Fig.  155,  the 
violet  band  is  highest, 
while  the  red  band  is 
lowest.  The  reason  is 
that  violet  light  is  bent 
mosfc  by  the  prism,  and 
red,  least.  The  order  of 
the  colors  will  be:  violet, 
indigo,  blue,  green,  yellow,  orange,  and  red.  The  initial 
letters  make  the  fanciful  word  VIBGYOR. 

When  platinum,  iron,  etc.,  are  heated,  they  first  become  red  hot,  and 
last  of  all  white  hot.  This  suggests  that  we  get  the  red  rays  first  because 
they  have  the  slowest  rate  of  motion.  Only  when  the  temperature  has 
risen  are  the  violet  rays  added  which  are  necessary  to  give  pure-white 
light.  The  red  rays  have  the  longest  waves;  the  violet  waves  are 
shorter,  but  move  much  more  rapidly. 

APPROXIMATE  LENGTH  OF  LIGHT  WAVES,  IN  MILLIMETERS 

Violet. 000397      Yellow 000589 

Indigo 000431      Orange 000656 

Blue 000480      Red 000688 

Green 000527 

If  a  reversed  prism  is  placed  so  as  to  catch  the  colored 
bands  produced  by  the  first  prism  (Fig.  156),  the  colors 


THE  RAINBOW  161 

will  be  brought  together  again,  and  the  rays  produced 
will  be  white,  as  they  were  before  refraction.  So  we  can 
prove,  both  by  breaking  up  white  sunlight  and  by  putting 
its  colored  parts  together,  that  it  is  composed  of  many 
rays  of  different  colors.  The  colored  band  produced  by 
the  single  prism  is  called  the  solar  (i.  e.,  the  sun's)  spectrum. 
It  was  first  studied  with  great 
care  by  Isaac  Newton,  in 
1672. 

FIG.  156. 

i  or\      TO.        T>     *     l»  TU  ~        Reversed  Prism.     Sunlight  that  has  been 

loll,      ine    KainDOW. ine  broken  up  can  be  recombined  to 

,,  ,  give  white  light. 

finest  solar  spectrum  we  see 

in  Nature  is  the  rainbow.  In  order  to  see  a  rainbow  we 
must  look  at  falling  rain,  and  the  sun  must  be  behind  us, 
and  42  degrees,  or  less,  from  the  horizon.  Half  the  dis- 
tance from  the  zenith  (c/.  §  177)  to  the  horizon  is  45  de- 
grees. On  a  small  scale  a  rainbow  may  often  be  seen  in  the 
spray  of  a  waterfall  or  of  a  lawn  sprinkler.  In  Nature  two 
bows  are  often  seen  together:  a  primary  one,  red  on  the 
outside  of  the  arch  and  violet  on  the  inside,  and  a  secon- 
dary one,  outside  the  primary  one,  and  with  the  colors  of 
the  primary  rainbow  in  reversed  order. 

In  forming  a  rainbow  each  drop  of  water  acts  both  as  a  lens  and  as 
a  mirror.  It  refracts  the  sun's  rays  as  they  enter  the  drop,  reflects 
them  from  side  to  side  within  the  drop,  and  then  refracts  them  as  they 
re-enter  the  air. 

From  the  outside  of  the  rainbow  arch  only  red  rays  reach  our  eyes. 
The  drops  inside  the  arch  send  to  us,  in  order,  orange,  yellow,  green, 
blue,  and  indigo  rays.  The  lowest  drops  send  the  violet  rays. 

A  halo,  or  ring  of  light,  around  the  moon  or  the  sun  is  probably  due 
to  a  similar  bending  of  light  rays  by  the  thin,  icy  clouds  of  the  upper 
part  of  the  atmosphere. 


162 


LIGHT  AND  SOUND 


heat  (cf.  §  183) 


181.  Absorption  of  Light;  Color. —  Certain  substances 
do  not  allow  light  to  pass  through  them,  and  do  not 
reflect  it;  what,  then,  becomes  of  the  light?    We  say  it  is 
absorbed  (§173).    It  is  really  changed  almost  entirely  into 

Lampblack,  or  soot,  is  a  good  absorber 
of  light;  silver  is  an  almost  perfect  re- 
flector (cf.  §§57  and  175;  also  Fig. 
157). 

We  see  most  objects  by  the  light  they 
reflect  (cf.  §§  165  and  174).  The  color 
of  an  object  thus  depends  upon  the  color 
of  the  reflected  rays,  or,  in  the  case  of  a 
transparent  body,  upon  the  color  of  the 
light  that  passes  through  the  body.  A 
red  body  sends  red  rays  to  the  eye,  and 
absorbs  all  other  rays.  If  it  reflects 
nearly  all  rays,  it  is  light  gray.  If  it 
absorbs  all,  it  is  black. 
Two  colors  that  yield  white  light  when  mixed  are  called  comple- 
mentary colors.  Such  are  red  and  blue-green,  yellow  and  blue-indigo, 
orange  and  light  blue,  green-yellow  and  violet.  Color  is  not  really  a 
property  of  bodies,  but  a  sensation  which  they  produce  upon  ourselves. 
What  we  call  color  is  the  sensation  that  a  body  produces  when  we  see  it 
in  ordinary  daylight.  We  all  know  how  different  the  same  colors  ap- 
pear in  daylight,  gas  light,  and  the  electric  arc  light.  A  blue  ribbon  will 
not  appear  blue  unless  the  light  by  which  it  is  illuminated  contains 
blue  rays.  Daylight  contains  blue  rays.  But  the  light  of  sodium 
vapor  (cf.  §  109)  contains  only  yellow  rays.  In  such  light  all  objects 
are  either  yellow  or  black.  For  the  same  reason  a  blue  object  held  in 
the  red  light  of  a  photographer's  "  dark  room  "  appears  black. 

182.  The  Sky  and  Its  Colors.—  The  normal  color  of  the 
sky  is  blue,  except  when  the  atmosphere  contains  too 


FIG.  157. 

Two  Air  Thermometers. 
The  air  in  the  black- 
ened bulb  becomes 
warmer  than  that  in 
the  colorless,  or  sil- 
vered, one;  the  black 
bulb  absorbs  the  more 
light  and  heat. 


CHANGE  OF  LIGHT  INTO  HEAT 

much  dust.  Atmospheric  dust  may  be  ordinary,  solid 
dust,  or  fine  particles  (mist)  of  water  or  ice  (cf.  §  268). 
Sunlight  dispersed  by  this  dust  is  " white' '  daylight  (cf. 
§§  173  and  176).  Near  the  sun  and  near  the  horizon  the 
sky  is  ordinarily  light  gray.  Sunrise  and  sunset  colors 
are  due  to  the  rays  that  are  refracted  least  (cf.  §  179) ; 
hence  the  indigo  and  blue  of  the  zenith  shade  into 
yellow,  orange,  and  red  near  the  horizon. 

Sky  coloring  is  caused  not  only  by  reflection  and  refraction,  but  also 
by  an  effect  which  thin  clouds  of  fine  particles  have  in  breaking  up  sun- 
light into  its  spectrum.  The  same  effect  is  produced  by  a  glass  plate 
ruled  with  many  parallel  lines,  say  15,000  to  the  inch.  The  phenome- 
non is  called  diffraction.  As  with  the  prism,  violet  rays  are  bent  most 
and  red  rays  least. 

In  1883  the  volcano  of  Krakatoa,  Java,  suffered  a  violent  explosion, 
and  so  much  dust  was  driven  into  the  upper  air  that  it  spread  around 
the  whole  globe.  It  produced  brilliant  sunset  effects  for  3  years. 

183.  Change  of  Light  into  Heat. —  From  the  study  of 
the  spectrum  we  learned  that  the  violet  rays  move  most 
rapidly  and  the  red  least  rapidly.  Below  the  red  rays 
there  are  rays  moving  too  slowly  to  give  out  light  of  any 
color,  yet  having  a  great  deal  of  energy.  These  long 
waves  can  be  changed  into  heat  just  as  light  waves  can. 
Glass  will  not  cut  off  the  light  waves,  but  it  will  cut  off  the 
longer  heat  waves.  We  can  prove  this  easily  by  holding 
a  pane  of  glass  between  the  hand  and  a  hot  stove.  Now, 
when  sunlight  has  been  absorbed,  and  is  then  radiated 
again  (cf.  §  66),  it  no  longer  consists  of  the  short  light 
waves,  but  of  the  long  heat  waves.  The  glass  of  green- 
houses or  hot-beds  thus  acts  as  a  trap  for  the  sun's  energy; 
for  it  permits  the  light  waves  to  pass  into  the  soil;  but 


164  LIGHT  AND  SOUND 

when  the  light  waves  have  been  changed  into  heat  they 
cannot  escape. 

The  water  vapor  and  impurities  of  the  air  act  like  glass 
in  making  prisoners  of  the  light  waves  and  thus  raising  the 
temperature  of  the  earth.  Without  this  the  chill  that 
would  follow  the  rapid  radiation  of  heat  from  the  earth 
would  quickly  put  an  end  to  all  animal  and  vegetable  life. 

184.  Light  and  Life.—  The  energy  of  the  sun  is  stored 
up  not  only  by  the  earth's  atmosphere,  but  also  by  the 
action  of  plants.    Plants  containing  chlorophyll,  the  green 
coloring  matter  of  our  common  vegetation,  are  able  by 
the  aid  of  sunlight  to  build  up  complex  organic  sub- 
stances, such  as  sugar,  starch,  cellulose,  etc.  (c/.  §  310). 
Plants  build  up  these  substances  out  of  carbon  dioxide 
and  water.    Oxygen  is  set  free  (cf.  §  52).    Energy  is  re- 
quired, for  this  is  chemical  work,  and  the  sun  supplies  it. 
When  the  material  produced  by  the  plant  is  afterwards 
used  as  fuel  or  food,  it  reunites  with  the  oxygen;  the  energy 
reappears  as  body  heat,  muscular  force,  etc.    In  a  very 
real  sense,  therefore,  plants  store  up  the  sun's  energy  for 
their  own  use  and  for  the  use  of  animals. 

185.  Exercises. 

1.  Stand  before  a  vertical  mirror,  and  look  at  the  image  of  your 
hand  while  you  write  your  name.    What  is  the  result?    Explain  it. 

2.  A  mirror  on  a  dresser  is  30  inches  above  the  floor.    How  do  you 
tilt  the  mirror  if  you  want  a  full  length  view  of  yourself?    Why  do  you 
step  back  from  the  dresser? 

3.  Why  is  the  broken  top  of  a  wave  white  ("  white  cap  "),  while  the 
unbroken  wave  is  blue,  green,  etc.? 

4.  If  you  lay  a  small  piece  of  thick  glass  over  the  middle  part  of  a 


COMPOUND  MICROSCOPE  165 

piece  of  wire,  and  then  look  at  the  wire  obliquely,  the  wire  seems  to  be 
broken  at  the  edges  of  the  glass.    Try  it,  and  give  the  reason. 

5.  If  you  look  obliquely  downward  at  a  fish  on  the  bottom  of  a  pond, 
is  the  fish  where  it  seems  to  be?    Is  it  nearer  you  or  farther  away? 
Draw  a  figure  to  show  why. 

6.  Why  do  we  see  the  sun  after  it  has  really  set,  and  before  it  has 
really  risen? 

7.  Investigation  has  shown  that  forest  fires  are  sometimes  caused  by 
glass  bottles  left  by  campers;  explain. 

8.  Do  we  ever  see  a  rainbow  at  midday?    Explain  why. 

9.  A  mercury  vapor  electric  lamp  contains  almost  no  red  rays.  What 
effect  has  this  upon  the  color  of  objects? 

10.  For  what  reasons  can  vegetables  be  raised  so  much  earlier  in  a, 
box  covered  with  glass  (a  "  cold  frame  ")  than  in  the  open  air? 

186.  Simple  Microscope,  or   Magnifying   Lens. — The 
simple  microscope  (Fig.  158)  consists  of  a  convex  lens 
that  will  bring  light  to  a  focus.    The  object  to  be  magni- 
fied (here  the  arrow  a  b)  is  placed 

between  this  focus  and  the  lens.  The 

figure  shows  that  the  image  (a'  b') 

will  appear  to  be  farther  from  the 

lens  than  the  object  is,  and  that  it     The  lens   £e*he  object  ap_ 

will  be  right  side  up  and  enlarged.  pear  ""tSSSSt0"  not 

187.  Compound  Microscope. — The  compound  micro- 
scope (Fig.  159)  consists  of  (1)  a  concave,  i.  e.,  hollowed 
out,  mirror  to  collect  and  direct  light  rays;  (2)  an  object 
lens,  or  objective ;  and  (3)  an  eye-piece.    The  inside  of  the 
microscope  tube  is  black,  to  prevent  light  from  being  re- 
flected back  and  forth. 

The  object  to  be  magnified  (a  b}  is  fastened  in  a  glass  "  slide,"  and 
is  lighted  up  by  rays  directed  by  the  mirror.    The  rays  from  the  object 


166 


LIGHT  AND  SOUND 


then  pass  through  the  object  lens,  and  produce  a  reversed  and  inverted 
image  near  the  eye-piece.  Just  as  the  simple  magnifying  lens  enlarges 
an  object  placed  near  it,  so  the  eye-piece  enlarges  the 
image  a  b' ,  and  it  appears  to  be  further  magnified  to 
the  size  a"  b"  (read  this:  a  second,  b  second). 


Eye  ,PTece 


188.  The  Camera. — The  camera  (Fig. 
160)  consists  of  a  dark  box  having  a  movable 
screen  of  ground  glass  (S).  The  tube  con- 
tains a  convex  lens.  The  image  of  the  object 
appears  upon  the  screen,  and  may  be  looked 
at  through  0.  When  the  image  has  been 
"  focused  "  on  the  screen,  a  "  sensitized  " 
film  or  glass  plate  is  put  in  place  of  the 
screen.  The  chemical  action  of  light 
"  prints  "  a  picture  of  the  object  upon  the 
film  or  plate. 

The  sensitive  film  or  plate  is  made  by 
completely8. image  covering  B>  sheet  of  gelatine  or  of  glass  with 
some  compounds  that  are  easily  decom- 
posed by  light.  Usually  these  are  silver  chloride  or  silver 
bromide.  After  the  film  or  plate  has  been  exposed  to  light 
from  the  object,  the  image  is  still  invisible.  It  must  be 
"  developed"  by  means  of  a  solution  of  pyrogallic  acid, 
or  some  other  "  developer."  Finally  the  image  is  "  fixed." 
Fixing  consists  in  removing 
the  unchanged  silver  salt. 
The  material  used  is  generally  o 
sodium  thiosulphate,  known  | 
popularly  as 


Objective 


FIG.  159. 

The  compound 
microscope  makes 
an  object  appear 
much  larger,  but 


hypo.3 


The  result  of  these  operations  is 


FIG.  160. 

The  camera  is  a  device  for  focusing  the 
clear  image  of  an  object  upon  a  sensi- 
tive plate  or  film. 


HOW  SOUNDS  ARE  MADE  AND  CARRIED  167 

the  negative  (Fig.  161).  In  it  the  light  parts  of  the  object  are  dark 
(opaque),  and  the  dark  parts  are  light.  The  photographer  "  prints  " 
the  positive  picture  by  placing  the  negative  over  sensitive  paper  con- 
taining silver  chloride,  and  exposing  the  two  for  some  time  to  sunlight. 
The  paper  will  then  be  changed  as  the  negative  was.  But  as  the  dark 
parts  of  the  negative  cut  off  the  light,  while  the  lighter  parts  permit 


FIG.  161. 
Negative  and  Positive  Photograph.     Negative  by  H.  L.  Schall. 

it  to  pass  through,  the  positive  "print"  contains  light  and  shade  in 
the  same  relation  as  the  object  photographed. 

189.  How  Sounds  are  Made  and  Carried. —  Just  as  light 
is  the  cause  that  affects  the  optic  nerve  and  gives  us  sight, 
so  sound  is  the  cause  that  affects  the  nerve  of  the  ear  and 
causes  hearing.  All  sound  is  due  to  the  motion  of  some 
portion  of  matter.  When  a  violin  string  is  producing  a 
note,  it  is  moving  rapidly  back  and  forth.  We  can  prove 
this  by  touching  the  string  lightly  with  the  finger.  We 
can  prove  the  same  thing  in  the  case  of  a  sounding  tele- 
phone or  door  bell.  When  we  speak  or  sing,  we  force  air 
through  the  slit  between  the  vocal  cords  (cf.  §  389),  and 
set  them  into  rapid  motion.  When  a  vibrating  tuning 


168 


LIGHT  AND  SOUND 


fork  is  put  into  water,  it  throws  the  water  into  sprays; 
this  shows  that  its  sounding  is  due  to  its  motion  (Fig.  162). 

Sounds  are  ordinarily  carried  by  the  air.  If  an  electric 
bell  is  placed  inside  a  vessel  of  air  (Fig.  163),  and  the  air 
is  nearly  all  removed  by  an  air  pump,  the  sound  given 
out  by  the  bell  is  feeble;  but  it  becomes  stronger  again 
when  air  is  admitted.  This  shows  that  a  vacuum  would 
not  carry  sound.  But  other  kinds  of  matter  besides 
air  carry  sound.  Thus  the  tap  of  a  pencil  or  the  scratch 
of  a  pin  against  a  long  steam  pipe  is  heard  readily,  if  we 
put  the  ear  close  to  the  pipe.  Iron  conducts  sound 
better  than  air.  Water  is  also  a  better  sound  conductor 

than  air:  the  clashing  together  of  two  stones  under  water  produces  a 

louder  sound  than  in  air.    In  air  at  0°  C. 


Fia.  162. 
A  sounding 
body    is    in 
rapid  vibra- 
tion. 


sound  travels  about  1,100  feet  in  a  second; 
in  water,  about  4,600  feet,  and  in  iron, 
about  17,000  feet. 


-f- 


Fia.  163. 

A  bell    ringing   in    a   vacuum 
would  give  forth  no  sound. 


190.  Sound  Waves. —  When  a 
sound  is  produced  (Fig.  164),  it  is 
heard  in  all  directions.  This  sug- 
gests to  us  that  sound  waves  start 
as  small  spheres  which  get  larger 
and  larger  as  they  move  outward  from  the  sounding 
body.  But  as  the  sphere  grows  larger,  more  and  more  air 
must  be  set  in  motion.  Naturally  the  motion  of  a  given 
volume  of  the  air  must  become  smaller  and  smaller.  Fi- 
nally the  motion  of  the  air  is  too 
small  to  affect  the  ear.  We  say  the 
sound  "  dies  out  "  with  distance. 
FIG.  164.  How  does  the  air  move  when  it 

s?ngnd8pwhaevrf,;8ptheelra8iseaSegr:    carries  sound?    It  caimot  go  as  in  a 

na^compressed  and  e*- 


ECHOES  169 

movement  of  a  body  of  air;  for  we  do  not  feel  any  motion 
of  the  air  from  a  sounding  body.  To  understand  the  for- 
mation of  sound  waves  we  must  remember  that  air  is  elastic; 
that  is,  it  can  be  compressed,  but  will  expand  again  when 
released.  The  sudden  jar  given  the  air  by  a  bell  (Fig.  164) 
pushes  the  air  particles  near  the  bell  forward,  producing  a 
layer  of  compressed  air.  This  layer  then  expands,  and 
in  doing  so  gives  a  rapid  push  to  the  next  layer  of  air. 
The  sound  wave  thus  proceeds  outward  as  a  series  of 
short,  rapid  compressions  and  ex- 
pansions of  air. 

With  a  row  of  elastic  balls  (Fig.  165)  we 
can  illustrate  the  way  in  which  air  particles 
can  give  up  their  motion  without  going 
forward.  If  we  draw  aside  one  of  the  balls, 
and  let  it  fall  against  the  row,  it  gives  its 
motion  to  its  neighbor.  This  gives  its  fow.  of  balls:  onlv  the  last 

ball  actually  moves  forward. 

motion  to  the  next  ball,  and  so  on  down  the 

line.    Only  the  last  ball,  which  has  no  ball  to  which  it  can  give  its 

motion,  actually  moves  forward. 

191.  Echoes. —  Sound  waves  are  reflected  as  light  waves 
are  (cf.  §  174).  If,  on  a  quiet  day,  we  shout  toward  some 
wall,  or  barn,  or  cliff,  our  shout  may  be  returned  to  us  as 
an  echo.  To  succeed  we  must  be  far  enough  away  to  per- 
mit the  shout  to  cease  before  the  reflected  sound  can  come 
back.  In  a  small  room  the  echo  blends  with  the  original 
sound,  and  we  do  not  notice  it;  but  in  a  large  room  or 
hall  the  echo  of  one  word  or  sentence  may  come  back  just 
as  another  is  being  spoken.  The  result  is  a  confused  mix- 
ture of  sounds.  Echoes  are  often  prevented  by  the  hang- 
ing of  curtains  or  wires  across  the  room.  These  break  up 
the  disturbing  sound  waves. 


170  LIGHT  AND  SOUND 

192.  Noise  and  Tone. — We  distinguish  clearly  between 
noises,  which  come  from  the  confused  mingling  of  sound 
waves,  and  tones,  which  are  the  result  of  a  rapid  succession 
of  waves,  all  of  the  same  sort,  and  coming  at  regular  in- 
tervals.   It  is  this  regularity  that  makes  musical  sounds 
pleasant  to  the  ear.     By  striking  hard  bodies,  such  as 
dishes,  stones,  wires,  car  wheels,  etc.,  we  find  that  each 
has  its  own  definite  tone. 

By  the  pitch  of  a  tone  we  mean  whether  it  is  high  or  low. 
Pitch  is  caused  by  the  frequency  of  the  vibrations  of  what- 
ever causes  the  sound.  "  Middle  C  "  of  a  piano  is  brought 
about  by  a  wire  that  vibrates  256  times  in  a  second.  The 
range  of  the  human  voice  is  from  about  80  vibrations 
(lowest  bass)  to  about  1000  vibrations  (high  soprano)  in  a 
second. 

We  can  hear  sounds  due  to  a  much  greater  frequency  than  we  can 
produce.  Thus,  the  high  notes  of  a  violin,  the  noise  of  a  cricket,  and 
the  whistle  of  a  locomotive  are  due  to  thousands  of  vibrations  in  a 
second.  When  a  sound  comes  from  more  than  40,000  vibrations  per 
second,  the  human  ear  can  no  longer  hear  it. 

193.  The    Telephone. — The    principle    according    to 
which  the  telephone  "  works  "  is  shown  in  Fig.  166.    M 
and  TV  are  two  permanent  magnets  placed  inside  the  wire 
coils  B  and  C.    The  circuit  is  through  the  coils,  the  wire 
connecting  them,  and  the  earth.     Before  each  magnet 
there  is  a  thin,  iron  disk  (D  and  E) .    If  we  make  a  sound 
in  front  of  D,  the  sound  waves  in  the  air  make  the  disk 
vibrate.     As  D  moves  back  and  forth  in  the  "  lines  of 
force  "  (cf.  §  138)  of  its  magnet  (M),  it  induces  currents 
(cf.  §  160)  in  the  coil  B.    These  currents  are  carried  along 
the  wire,  and  appear  in  the  coil  C.    Here  they  cause  move- 


SUMMARY 


171 


FIG.  166. 
The  Simple  Telephone. 


ments  of  the  lines  of  force  of  the  magnet  A7,  and  produce 
vibrations  in  the  disk  E.  The  vibrations  of  E  are  just 
like  those  of  Z),  and  reproduce  the  sound  we  made  at  the 
other  end  of  the  line. 

In  the  modern  telephone  the  "  return  circuit"  is 
through  a  second  wire 
instead  of  through  the 
earth.  The  receiver  is 
like  the  simple  disk  of 
the  figure,  but  the  speak- 
ing instrument  ("trans- 
mitter") is  more  complex. 
The  telephone  was  in- 
vented in  1875  by  Alexander  Graham  Bell,  of  Washington, 
and  Elisha  Gray,  of  Chicago. 

194.  Summary. — A  visible  body  is  either  self-luminous  or  illuminated. 

Bodies  may  be  transparent,  translucent,  or  opaque. 

Light  is  the  cause  that  produces  sight.  It  moves  in  straight  lines  at 
a  speed  of  186,000  miles  a  second. 

An  image  formed  through  a  small  opening  is  inverted. 

A  shadow  formed  from  a  point  of  light  is  distinct,  and  composed  of 
an  umbra  alone.  A  shadow  from  a  luminous  surface  has  both  umbra 
and  penumbra. 

An  eclipse  of  the  sun  occurs  when  the  earth  is  within  the  moon's 
shadow.  An  eclipse  of  the  moon  occurs  when  the  moon  is  in  the 
earth's  shadow. 

Intensity  of  light  is  given  in  candle  power.  A  photometer  is  an  in- 
strument for  finding  when  the  intensity  of  light  from  two  luminous 
bodies  is  the  same. 

Light  striking  a  body  may  be  reflected,  dispersed,  or  absorbed;  or 
it  may  pass  through  the  body. 

Light  is  reflected  at  the  same  angle  as  that  at  which  it  strikes  the 
reflecting  surface,  but  in  a  different  direction. 


172  LIGHT  AND  SOUND 

A  plane  mirror  gives  an  image  that  is  right  side  up,  but  has  the  right 
and  left  sides  reversed. 

We  see  an  object  in  the  direction  which  its  light  has  as  it  enters 
the  eye. 

Daylight  is  dispersed  sunlight. 

Light  that  passes  from  one  substance  to  another  of  a  different 
density  is  refracted.  Because  of  refraction,  objects  in  water  are  not 
seen  in  their  correct  positions,  and  the  heavenly  bodies  seem  higher 
above  the  horizon  than  they  really  are. 

A  lens  with  convex  faces  brings  light  rays,  heat  rays,  and  sound 
waves  to  a  point,  or  focus. 

White  light  is  a  mixture  of  many  colors.  It  is  broken  up  into  its 
primary  colors  by  a  prism.  The  band  of  colors  produced  by  sunlight  is 
called  the  solar  spectrum.  A  rainbow  is  a  spectrum  on  a  large  scale. 

The  color  of  a  body  is  due  to  the  rays  it  reflects.  It  absorbs  rays  of 
all  other  colors. 

Light  rays  are  changed  into  heat  rays  when  they  are  absorbed  by  the 
earth  and  then  given  off. 

Plants  having  chlorophyll  use  sunlight  to  prepare  sugar,  starch,  etc., 
out  of  carbon  dioxide  and  water. 

The  simple  microscope  gives  an  enlarged,  natural  image. 

The  compound  microscope  consists  of  a  mirror,  an  objective,  an 
eye-piece,  and  a  tube.  It  gives  an  enlarged  image  which  is  completely 
reversed. 

The  camera  consists  of  a  dark  box,  a  screen,  and  a  lens.  It  gives  an 
inverted,  reversed  image  of  reduced  size. 

Sounds  are  ordinarily  carried  by  the  air,  but  they  may  be  carried 
by  water,  metals,  wood,  etc. 

Sound  waves  extend  outward  from  the  sounding  body  as  enlarging, 
spherical  layers  in  which  air  is  alternately  compressed  and  expanded. 

Echoes  are  reflected  sound  waves. 

Noises  are  sound  waves  coming  at  irregular  intervals.  Tones  are 
waves,  all  of  the  same  kind,  and  coming  at  regular  intervals. 

Pitch  depends  upon  the  frequency  of  vibration. 

The  telephone  is  constructed  on  the  principle  that  vibrations  of  an 
iron  disk  in  the  field  of  one  magnet  will  produce  corresponding  vibra- 
tions in  an  iron  disk  placed  in  the  field  of  another  magnet  far  away. 


EXERCISES  173 

195.  Exercises. 

1 .  Why  does  the  photographer  use  red  light  in  his  dark  room? 

2.  If  you  were  to  hold  a  suspended  pith  or  cork  ball  near  a  sounding 
tuning  fork,  what  would  happen? 

3.  Suggest  why  it  is  so  much  harder  for  a  speaker  to  be  heard  in  the 
open  air  than  in  a  hall. 

4.  A  circular  saw  has  a  certain  note  when  revolving  rapidly.    Why 
does  the  pitch  of  the  sound  fall  when  the  saw  cuts  into  a  board? 

5.  Why  is  the  ringing  of  a  bell  so  much  clearer  when  the  sound 
comes  "  with  "  the  wind  than  when  it  comes  "  against "  the  wind? 
How  does  the  wind  affect  the  shape  of  the  sound  waves? 

6.  When  is  a  room  more  likely  to  have  echoes,  when  full  of  people, 
or  when  empty?    Why? 

7.  How  are  the  marks  upon  a  graphophone  "  record  "  changed  into 
sound?    How  are  the  records  made? 

8.  How  can  sound  waves  be  carried  through  a  speaking  tube? 

9.  Of  what  are  "  chimes  "  constructed?     How  are  the  different 
notes  secured? 

10.  Why  can  you  hear  a  distant  carriage  better  by  putting  your 
ear  to  the  ground? 

11.  What  is  the  principle  of  the  yell  leader's  megaphone? 


CHAPTER  X 

SIMPLE  MACHINES 

196.  Need  of  Machines. —  Man  uses  a  multitude  of 
devices,  or  tools,  to  enable  him  to  do  his  work  to  better 
advantage.     Thus,  he  pries  a  stone  or  a  log  instead  of 
lifting  it.    If  he  needs  to  raise  stones  or  bricks  to  the  top 
of  a  building,  he  employs  a  pulley  with  a  rope  over  it ;  by 
pulling  downward  on  the  rope,  he  pulls  the  weight  upward. 
He  splits  logs  with  wedge  and  axe,  and  ploughs  with  a  slop- 
ing knife,  or  ploughshare.    If  he  has  to  raise  barrels  into  a 
wagon,  he  rolls  them  up  a  sloping  board  instead  of  lifting 
them.    Wherever  possible,  he  puts  a  wheel  or  roller  under 
a  heavy  object,  so  that  he  can  move  it  without  lifting  it. 
Finally,  in  order  to  fasten  pieces  of  cloth  or  skin  together, 
he  uses  a  needle  or  an  awl.    Since  the  thickness  of  this  tool 
increases  very  gradually,  a  little  pushing  forces  the  fabric 
apart,  and  makes  a  hole  for  the  thread.     The  forms  of 
tools  have  become  more  ingenious  and  complicated  with 
man's  progress  in  civilization,  but  the  simple  principles 
have  been  known  for  ages.     These  principles  are  repre- 
sented by  six  simple  contrivances,  or  machines : 

(1)  The  Lever.  (4)  The  Inclined  Plane. 

(2)  The  Pulley.  (5)  The  Wedge. 

(3)  The  Wheel  and  Axle.  (6)  The  Screw. 

197.  Law  of  Machines. —  None  of  these  machines  nor 
any  of  their  improved  forms  can  originate,  or  create,. 

174 


LAW  OF  MACHINES  175 

any  energy.  They  simply  make  it  possible  for  us  to  apply 
force  in  a  convenient  direction,  or  at  a  convenient  place. 
Or  they  make  it  possible  for  us  to  exchange  a  small  force 
exerted  through  a  considerable  distance  for  a  much  larger 
force  exerted  through  a  correspondingly  shorter  distance. 
Thus,  we  give  the  head  of  a  screw  driver  one  complete 
turn  in  order  to  get  the  screw  to  move  forward  only  the 
distance  between  two  successive  threads;  but  the  force 
we  exert  in  overcoming  the  cohesion  of  the  wood  is  enor- 
mously greater  than  that  which  we  ap- 
ply to  the  head  of  the  screw  driver. 
Again,  we  probably  could  not  draw  a 
nail  out  of  a  board  by  pulling  with  all 
our  might,  yet  by  the  use  of  a  claw 


hammer  (Fig.  167)  we  need  to  put  forth 


FIG.  167. 


only  a  small  effort  to  do  the  work.    But      A  claw  hammer  is  a 

machine. 

we  must  remember  that  in  using  ma- 
chines we  are  making  an  exchange,  not  getting  something 
for  nothing. 

The  exchange  we  make  in  using  a  sewing  machine  is  the 
opposite  of  that  which  we  make  in  the  screw  and  the 
hammer.  Sewing  by  hand  is  hard,  not  because  it  requires 
much  strength,  but  because  it  is  slow.  With  a  sewing 
machine  the  seamstress  can  exchange  her  strength  for 
greater  speed. 

The  law  of  machines  is  merely  the  statement  of  the 
exchange  we  make  in  every  machine.  If  we  multiply 
the  power  exerted  (stated  in  weight  units)  by  the  dis- 
tance through  which  the  source  of  the  power  moves, 
the  product  is  just  equal  to  the  product  obtained  when 
we  multiply  the  resistance  overcome,  or  the  weight 


176 


SIMPLE  MACHINES 


lifted,  by  the  distance  through  which  the  resisting  object, 
or  weight,  moves. 
Power  X  power  distance  =  weight  X  weight  distance. 

198.  The  Lever. —  The  claw  hammer,  pitchfork,  and 
crowbar  are  common  forms  of  the  lever.  The  fixed 
support  on  which  the  lever  rests  is 
called  the  fulcrum.  If,  in  Fig.  168, 
the  distance  from  the  fulcrum  (F)  to 
the  point  at  which  the  weight  (R)  is 
attached  is  1  foot,  and  the  distance 
from  F  to  the  point  (P),  where  the 
power  is  applied,  is  2  feet,  then  the  weight  that  can  be 
lifted  at  R  is  twice  the  power  applied:  40  pounds  at  P 
can  support  80  pounds  at  R.  If  the  distance  from  F  to  R 
is  3  inches,  and  that  from  F  to  P  is  51 
inches,  then  40  pounds  at  P  can  sup- 
port 680  pounds  at  R. 


FIG.  168. 
A  Lever  of  the  First  Class- 
The  fulcrum  is  between 
the  force  exerted  and  the 
resistance  to  be  overcome. 


FIG.  169. 
Fish  Scales:    a  Lever  of 
the  First  Class. 


The  balances  (Fig.  9)  are  a  lever.    If  the 

two  arms  are  of  equal  length,  equal  weights  in 

the  two  pans  will  just  support  each  other. 

In  fish  scales  (Fig.  169)  the  arm  holding  the  pan  is  the  shorter, 

hence  a  heavy  object  on 
this  pan  can  be  supported 
—  ' '  weighed  "  —  by  a  small 
weight  on  the  longer  arm. 
The  weighted  gate  (Fig.  170) 
and  the  well  sweep  (Fig.  171) 
are  other  examples  of  the  lever. 


FIG.  170. 

Weighted  Gate.  The  stone  nearly  balances  the 
gate,  so  that  very  little  effort  is  required  to 
lift  the  gate. 


199.  Classes  of  Levers. —  We  divide  levers  into  three 
classes  according  to  the  way  in  which  the  fulcrum,  the 


CLASSES  OF  LEVERS 


177 


FIG.  171. 

Well  Sweep :  a  Lever  Used  in  Raising 
Water  from  a  Well.  Courtesy  of 
the  Ansco  Co. 


power,  and  the  resistance  are 
placed  with  regard  to  one  an- 
other. In  the  crowbar  and 
balance  the  fulcrum  is  between 
the  other  two.  Such  a  lever  is 
of  the  first  class. 

In  the  nut-cracker  (Fig.  172) 
the  resistance  (the  nut)  is  be- 
tween the  other  two  :  the  fulcrum 
is  at  one  end.  This  is  a  lever  of 
the  second  class  (Fig.  173). 

A  wheelbarrow  is  also  of  the 
second  class.    The  fulcrum  is  the 
axle  of  the 
wheel,  the 

power  is  applied  to  the  handles,  and 
the  weight  is  between  them.  The 
rule  of  machines  applies  here,  just  as 
in  levers  of  the  first  class.  In  making 
the  calculation  we  will  not  count  the  weight  of  the  wheel- 
barrow. If  you  place  a  piece  of  ice, 
weighing  100  pounds,  1  foot  from 
the  axle  of  the  wheel,  and  grasp  the 
handles  5  feet  from  the  axle,  you 
need  exert  a  force  of  only  20  pounds 
to  lift  the  ice. 

Levers  of  the 

third  class  have  the  fulcrum  at  one 
end,  just  as  those  of  the  second  class 
nave>  but  the  power  is  applied  be- 
tween  the  resistance  and  the  fulcrum 


FIG.  173. 

Lever  of  Second  Class.  The 
resistance  is  between  the 
fulcrum  and  the  power. 


Lever  of  'the'  Third  class. 
'18  at  P 


178  SIMPLE  MACHINES 

(Fig.  174).  The  tread  of  a  grindstone  and  of  a  weaving 
loom  are  examples  of  third  class  levers.  So  is  the  human 
forearm  (Fig.  277,  §  355). 

200.  Exercises. 

1.  To  what  class  of  levers  do  scissors  belong?     In  cutting  thick 
cloth,  or  a  wire,  with  shears,  do  you  put  the  cloth,  or  wire,  at  the  tips 
of  the  shears  or  near  the  rivet?    Why? 

2.  What  kind  of  a  lever  is  a  pair  of  sugar  tongs?    The  oar  of  a  boat? 
The  handle  of  a  hoe?    A  pitchfork?    A  pump  handle? 

3.  If  you  were  using  a  crowbar  to  roll  a  log  along  the  ground,  how 
would  you  use  the  bar  as  a  lever  of  the  first  class?    How  as  a  lever  of  the 
second  class? 

4.  If  you  support  a  5  Ib.  weight  at  one  end  of  a  bar  3  ft.  long  by 
means  of  a  10  Ib.  weight  at  the  other  end,  where  must  the  fulcrum  be 
placed? 

5.  An  oar  is  7  ft.  long,  and  the  handle  is  1  ft.  from  the  oarlock.    How 
far  is  the  end  of  the  blade  from  the  oarlock?    A  boy  pulls  on  the  handle 
with  a  force  of  25  Ibs.;  what  force  does  the  oar  blade  exert  on  the 
water?    Would  there  be  any  advantage  in  having  the  oar  handle  2  ft. 
from  the  oarlock? 

6.  Why  is  an  oar  blade  made  so  broad?    Upon  what  property  of 
water  does  the  blade's  usefulness  depend? 

7.  When  a  woman  is  pushing  with  her  toes  against  the  treadle  of  a 
.sewing  machine,  where  is  the  power  as  regards  fulcrum  and  weight? 

What  kind  of  a  lever  is  the  treadle  in  this  case?  What 
kind  is  it  when  she  uses  her  heel?  In  which  case  does 
she  have  to  do  more  work?  How  is  the  treadle  attached 
to  the  driving  wheel? 


201.  Pulleys.  —  In  the  simplest  form  of  the 
pulley  (Fig.  175)  we  cannot  lift  more  than 


FIG.  175.  the  power  we  put  forth;  but  we  can  raise  the 
weight  by  pulling  downward.  Such  a  pulley 
is  used  for  hoisting  the  sails  of  a  ship,  or  for 


THE  WHEEL  AND  AXLE 


179 


raising  a  flag  on  a  flagstaff.  By  means  of  a 
second  pulley  a  horse  pulling  in  a  horizontal 
direction  can  raise  a  weight  vertically  upward 
(cf.  Fig.  20,  §  26). 

If  we  arrange  two  pulleys  as  in  Fig.  176,  two  cords 
support  the  weight,  while  only  one  is  supported  by  the 
power;    hence  a  power   of  1   pound  can 
support  a  weight  of  2  pounds.    We  get  this    and  One  Fixed 
advantage  because  the  cord  on  which  we 
pull  must  descend  twice  as  far  as  the  weight  rises. 
If  there^  are  three  cords  (Fig.   177)  supporting  the 
weight,  and  one  supported  by  the  power,  1  pound  can 
lift  3. 

FIG.  177.  202.  The  Wheel  and  Axle.— In  the  wheel 
and  axle  (Fig.  178)  the  power  applied  on  the 
wheel  must  move  a  distance 
equal  to  the  circumference  of  the  wheel, 
while  the  weight  attached  to  the  axle 
moves  only  the  circumference  of  the  axle. 
The  wheel  in  the  figure  has  a  circum- 
ference 3  times  that  of  the  axle;  therefore 

1  pound  on 
the  wheel 
will  support 
3  pounds 
on  the  axle. 

The  winch,  or  windlass  (Fig. 
179),  is  a  form  of  the  wheel 
and  axle  in  which  the  power  is 
applied  to  a  crank.  To  raise 
the  weight  a  distance  equal  to 
winch  used  for  Raising  of  water.  the  circumference  of  the  axle, 


FIG.  178. 
Wheel  and  Axle. 


180 


SIMPLE  MACHINES 


the  power  must  be  exerted 
through  one  complete  turn  of 
the  crank.  A  derrick  (Fig.  180) 
consists  of  a  winch  and  a 
system  of  cog  wheels  and 
pulleys. 

203.  The  Inclined 
Plane. —  In  climbing  a 
hill  or  mountain  we  pre- 
fer •  to  go  up  gradual 
slopes  instead  of  steep 
ones,  because  in  this  way 
we  can  raise  the  weight  of  our  bodies  with  much  less 
effort.  But  in  doing  so  we  make  an  exchange:  we  travel  a 
much  greater  actual  distance  than 
if  we  go  "  straight  up."  So,  if 
we  wished  to  raise  a  200  pound 
barrel  from  the  ground  to  a 
wagon,  we  might  lift  it  up  directly; 
but  an  easier  way  would  be  to  roll 
it  up  an  inclined  plane  (Fig.  181).  If  the  plane  were  10 
feet  long  and  3^  feet  from  the  ground  at  the  higher  end, 
the  force  required  to  push  the  barrel  up  the  plane  would 
be  1A  of  200,  or  66%  pounds.  We  roll  the 
barrel  3  times  as  far  as  we  wish  to  raise  it, 
but  we  need  exert  only  J^  of  the  force. 
This  is  the  effort  required  if  we  exert  force 
parallel  with  the  plane. 


FIG.  182.  204.  The  Wedge.— The  wedge   (Fig.    182)    is 

of  im-iinedplane?1      really  two  inclined  planes  with  their  bases  placed 


FIG.  181. 
Inclined  Plane. 


THE  SCREW 


181 


together.  It  is  made  of  hard  wood  or  of  iron,  and  is  used  to  split  logs 
and  stones,  or  sometimes  to  raise  a  heavy  weight.  If  the  length  of  the 
wedge  is  5  times  its  thickness,  we  drive  it  into  the  log  5  inches  in 
order  to  force  the  wood  apart  1  inch.  The  axe  is  a  wedge;  so  are  the 
pin  and  the  needle  (cf.  §  196). 

205.  The  Screw.  —  If  we  were  going  to  the  top  of  a 
lighthouse  100  feet  high,  we  might  climb  a  vertical  ladder 
or  rope,  01  we  might  go  up  gradually,  on  a  long  inclined 
plane,  rising,  say,  1  foot  in  every  10.  In  the  ascent  by  the 
inclined  plane  we  would  walk  1000  feet  in 
order  to  rise  100  feet.  The  most  compact 
way  of  arranging  an  inclined  plane  is  in  a 
spiral.  This  is  done  in  the  spiral  staircases 
of  many  lighthouses  and  towers. 

Now,  the  screw  (Fig.  183)  is  really  a 
long  inclined  plane  with  the  ascent 
arranged  in  a  spiral  instead  of  in  a  straight 

T  A  11     f  i  , 

line.     A  small  force  can  produce  a  large 

„-  'IT  n 

enect  with  the  screw;  for  the  power  must 

go  a  long  distance  in  order  to  make  the  screw  itself  ad- 

vance a  very  short  distance. 

The  distance  between  threads  is  called  the  "  pitch  "  of  the  screw. 
Suppose  that  a  screw  having  12  threads  to  the  inch  is  driven  by  a 
screw  driver  having  a  handle  2  inches  in  diameter. 
The  handle  has  a  circumference  of  2X31/?,  or  62/7 
inches.  The  handle  is  thus  turned  through  62/7 
inches  while  the  screw  advances  l/iz  of  an  inch. 
Hence  the  power  moves  about  75  times  (62/7  divided 
by  Vi2)  as  far  as  the  resistance  or  weight;  a  force  of 
3  pounds  applied  on  the  handle  will  exert  a  force  of 
about  225  pounds  on  the  threads  of  the  screw. 
The  screw  is  used  not  only  for  holding  pieces  of 


great  weights,  such 

as  wagons  or  houses, 

^or  short  distances. 


182  SIMPLE  MACHINES 

wood  or  metal  together,  and  for  lifting  weights,  but  also  for  producing 
great  pressure.  The  letter-copying  press  (Fig.  184)  and  the  vise  are 
screws  used  for  this  purpose. 

206.  Friction.—  The  law  of  machines  (cf.  §  197)  does 
not  turn  out  to  be  exactly  true  in  the  actual  use  of  a 
machine,  because  some  of  the  power  exerted  is  used  in 
overcoming  friction  (cf.  §  24).    But  while  friction  repre- 
sents lost  effort,  some  friction  is  usually  necessary  in  order 
that  a  machine  may   "  work."     Thus,   a  barrel  must 
"stick  "  slightly  to  an  inclined  plane,  or  we  cannot  roll  it 
up;  a  rope  passed  over  a  pulley  must  adhere  to  the  rim  of 
the  pulley,  or  the  pulley  wheel  will  not  turn  when  the 
rope  is  drawn  in.    We  all  know  how  difficult  it  is  to  walk 
upon  a  highly  polished  floor,  owing  to  the  lack  of  friction 
between  our  shoes  and  the  floor.     Also,  heavy  objects 
that  are  to  be  moved  horizontally  are  placed  on  rollers  or 
wheels,  if  possible,  because  rolling  friction  is  much  less 
than  sliding  friction.     The  wheelbarrow  illustrates  this 
admirably,  also  the  use  of  castors  on  bedsteads,  tables,  etc. 

207.  The    Sailboat. —  Few   discoveries   of   man   have 
helped  him  more  in  his  rise  to  civilization  than  his  ability 
to  travel  long  distances  by  water;  this  was  made  possible 
largely  by  his  discovery  of  the  use  of  sails. 

We  can  readily  understand  how  a  boat  can  sail  "  before 
the  wind":  the  sail  merely  provides  a  large  area  for  re- 
ceiving the  pressure  of  the  moving  air.  The  sailboat  not 
only  permits  us  to  sail  in  the  direction  of  the  wind,  but  it 
permits  us  to  exchange  rapid  motion  in  this  direction  for 
slower  motion  in  some  other  direction.  No  sailboat,  of 
course,  can  go  directly  against  the  wind. 


THE  SAILBOAT 


183 


Use  of  Keel. —  A  wind  blowing  against  a  boat  causes  it  to  move  in 

the  direction  of  the  wind;  that  is,  to  "  drift."    To  prevent  drifting 

we  provide  a   boat  with   a   "keel" 

or  a  "  centerboard."    A  keel  is  a  strip 

projecting  from  bow  to  stern  on  the 

bottom  of  a  boat.     A  centerboard  is  a 

movable  keel.     The  centerboard  can 

be  lowered  into  the  water  when  the 

boat  is  in  deep  water,  and  drawn  up 

within  the  boat  when  the  boat  is  in 

shallow  water.    We  can  illustrate  the 

action  of  the  keel  by  pushing  a  vertical 
board  side- 
wise  under 
water.  The 
water  re- 
sists being  pushed  out  of  the  way,  just  as  air 
does  (cf.  §  27). 

Use  of  Wind  by  the  Sail.—  The  sail  (Fig. 
186)  is  attached  so  that  it  can  be  let  out  at 
right  angles  to  the  keel,  or  "  hauled  in  "  until 
it  is  almost  parallel  with  the  keel.  Let  Fig. 
187  represent  a  boat  moving  in  the  direc- 
tion of  the  keel;  that  is,  forward.  The  wind 
is  coming  from  the  side,  at  right  angles  with 
the  keel.  Such  a  wind  is  called  a  "  beam 
wind."  It  is  plain  that  if  the  sail  were  let 
out  competely,  no  part 
of  the  wind  would  be 


FIG.  185. 

Course  of  a  boat  "beating  to  wind- 
ward." 


FIG.  186. 

A  Sloop  under  Full  Way. 
Courtesy  of  Dr.  C.  F. 
Millspaugh. 


caught,  and  there  could  be  no  forward  motion  of 
the  keel.  If  the  sail  were  drawn  in  completely, 
the  whole  pressure  of  the  wind  would  be  against 
the  keel,  and  there  would  be  only  a  sidewise 
motion,  provided  the  boat  was  not  capsized.  But 
if  the  sail  is  set  obliquely  with  the  keel,  as  in  Fig. 
187,  part  of  the  force  of  the  wind  is  used  in  push- 
ing the  boat  sidewise  (a  motion  resisted  by  the 


FIG.  187. 
Diagram  of  a  Sailboat. 


184 


SIMPLE  MACHINES 


Kite 


_  String 
FIG.  188. 


keel),  while  another  part  pushes  the  boat  forward.  The  more  efficient 
the  keel  is,  the  less  does  the  boat  drift;  the  "  closer  "  does  it  sail  "to 
the  wind." 

208.  The  Kite. —  While  in  the  sailboat  the  force  of  a 
horizontal  wind  is  changed  partly  to  a  force  acting  di- 
rectly forward,  in  the  kite  a  part  of  the 
wind's  force  is  made  to  act  vertically 
upward.  If  the  kite  (Fig.  188)  is  held 
i Raising  vertical,  it  gets  all  the  force  of  the  wind 
that  strikes  it,. and  moves  off  in  a  hori- 
zontal direction.  This  takes  place  when 
why  the  wind  Makes  a  the  kite  string  breaks  while  the  kite  is  in 

Kite  Rise.  ° 

the  air.  The  kite  is  then  only  a  falling 
body  (cf.  §  21),  acted  upon  by  the  wind  and  by  gravity. 
If  the  kite  were  held  horizontal,  it  would  catch  no 
part  of  the  wind,  like  a  boat  with  its  sail  parallel  with 
the  wind.  But  if  the  kite  is  inclined  to  the  wind,  the 
force  of  the  wind  is  divided  into 
two  parts,  one  of  which  presses 
against  the  kite,  and  is  resisted 
by  the  string;  while  the  other 
part  acts  vertically  upward,  and 
raises  the  kite  into  the  air. 


209.  The  Airship.  —  Airships 
may  be  of  the  balloon  type 
(Fig.  189),  which  rise  because 
they  are  filled  with  heated  air  or 
other  light  gases;  or  they  may 
be  aeroplanes  —  monoplanes, 
biplanes,  hydroplanes,  etc.  — 


FIG.   189. 

One  of  the  first  Dirigible  Airships  to 
Fly  in  America.  Note  the  whirling 
propellor  in  front.  Copyright, 
The  International  Stereograph 
Co.,  Decatur,  111. 


THE   WINDMILL  185 

which  rise,  as  the  kite  does,  because  of  the  resistance 
(inertia)  of  the  air  (Fig.  190).  Only,  while  the  kite  uses 
the  inertia  of  air  in  motion  (wind),  the  plane  airship  uses 
air  as  matter  which  resists  being  pushed  out  of  the  way. 

The  explanation  of  the  action  of  the  air  upon  the  aeroplane  is  prac- 
tically the  same  as  if  the  aeroplane  were  still,  and  the  air  were  in  rapid 


FIG.  190. 
A  Modern  Wright  Flyer.     Courtesy  of  Dr.  Orville  Wright. 

motion.  When  the  engine  forces  the  planes  rapidly  forward,  the  force 
(resistance)  of  the  air  acts  in  two  parts,  as  with  the  kite.  One  of  these 
parts  opposes  the  forward  movement  of  the  planes,  and  must  be  over- 
come by  the  engine.  The  other  portion  of  the  air's  resisting  force  acts 
vertically  upward,  and  raises  the  planes,  against  gravity,  into  the  air. 

210.  The  Windmill. —  One  of  the  reasons  why  farming 
has  developed  so  rapidly  in  recent  years  is  that  windmills 


186 


SIMPLE  MACHINES 


have  come  into  such  general  use  in  pumping  water  for  the 
uses  of  the  farm.  The  windmill  relieves  the  farmer  and 
his  family  from  the  drudgery  of  pumping  water,  and 
leaves  them  free  for  other  labor.  The  windmill,  like  the 
sailboat,  kite,  and  aeroplane,  works  upon  the  principle 
that  if  wind  strikes  a  plane  obliquely,  part  of  the  force  of 

the  wind  is  exerted  in  producing 
forward  (or  upward)  motion. 
In  the  windmill  the  planes  (sails) 
are  attached  to  a  hub  (Fig.  191) ; 
as  the  planes  move  forward,  the 
hub,  or  wheel,  revolves.  The 
"  pin-wheel "  we  used  when 
children  is  a  miniature  windmill. 

For  the  pumping  of  water,  the  re- 

FIQ  volving  wheel  is  attached  to  a  piston 

A  Dutch  Windmill.   Copyright  The  which  moves  up  and  down  in  a  pump 
JatTrrimnnotStereographC°-'  De-   fcf-  §  42);  water  is  thus  raised  out  of  a 

well  or   cistern.    On  windy  days  the 

windmill  pumps  the  water  into  a  raised  tank,  from  which  it  can  be 
drawn  when  there  is  no  wind,  and  the  mill  is  quiet. 

A  recent  article  states  that  a  village  in  Alaska,  far  within  the  Arctic 
Circle,  is  to  have  its  long  night,  of  six  months,  illuminated  by  electri- 
city. The  average  wind  velocity  at  the  village  is  20  miles  an  hour,  and 
a  large  windmill  will  operate  the  dynamo  that  gives  the  current  for  the 
light  (cf.  §  162). 

211.  Summary. —  The  complicated  machines  used  by  man  are  forms 
of  six  simple  machines:  the  lever,  pulley,  wheel  and  axle,  inclined 
plane,  wedge,  and  screw. 

A  machine  enables  man  to  exert  force  more  advantageously,  but  it 
does  not  create  any  energy. 

Power  x  distance  power  moves  equals  weight  x  distance  weight 
moves. 


EXERCISES  187 

Levers  are  of  three  classes: — 

(1)  The  fulcrum  is  between  the  weight  and  the  power. 

(2)  The  weight  is  between  the  fulcrum  and  the  power. 

(3)  The  power  is  between  the  fulcrum  and  the  weight. 
Pulleys  are  wheels  over  which  ropes  can  be  pulled. 

The  wheel  and  axle  is  a  form  of  the  lever  used  for  circular  motion. 

The  wedge  and  the  screw  are  really  forms  of  the  inclined  plane. 

Friction  prevents  us  from  getting  the  full  amount  of  work  out  of  a 
machine;  but  some  is  necessary  in  order  that  machines  may  work  at  all. 

A  sailboat  is  a  device  for  getting  some  forward  motion  out  of  any 
wind  except  one  that  is  "  dead  ahead." 

The  kite  gets  upward  motion  out  of  a  horizontal  wind. 

The  aeroplane  gets  upward  motion  by  the  pushing  of  its  obliquely- 
set  planes  horizontally  against  the  air. 

The  windmill  converts  a  horizontal  wind  into  circular  motion. 

212.  Exercises. 

1.  What  kind  of  a  machine  is  used  for  lifting  window  awnings? 
A  door  transom?    A  weighted  window  sash? 

2.  How  could  you  arrange  a  system  of  pulleys  so  that  by  pulling 
downward  with  a  force  of  20  Ibs.  you  could  raise  40  Ibs.? 

3.  If  the  crank  of  a  winch  (Fig.  179)  makes  a  circle  of  36  in.  while 
the  rope  is  wound  up  6  in.  for  each  complete  revolution  of  the  crank, 
how  much  force  must  I  exert  on  the  crank  to  lift  a  pail  of  water  weigh- 
ing 100  Ibs.? 

4.  What  kind  of  a  machine  is  a  nail,  a  coffee-grinder,  a  carpenter's 
brace  and  bit,  a  pendulum  bob,  a  snow  plow,  a  pin-wheel,  a  door  knob, 
a  spoon,  a  spade,  a  chisel? 

5.  How  do  you  hold  your  knife  and  your  fork  when  cutting  a  tough 
piece  of  meat?    What  kind  of  machine  are  these  implements  then? 
What  machine  are  the  tines  of  the  fork  and  the  blade  of  the  knife? 

6.  A  man  who  can  exert  a  force  of  100  Ibs.  wishes  to  raise  a  300  Ib. 
barrel  into  a  wagon  3  ft.  above  the  ground.    He  uses  an  inclined  board; 
how  long  must  it  be? 

7.  In  loading  a  wheelbarrow,  where  should  you  put  the  load  in  order 
to  make  the  force  needed  for  lifting  as  small  as  possible? 


CHAPTER  XI 


(Term^nTed    Fruit  Juice) 


ACIDS,  ALKALIES,  AND  CLEANING 

213.  Acids. —  We  learned  in  §  5  that  no  two  sub- 
stances have  exactly  the  same  special,  or  specific,  prop- 
erties. There  are,  however,  many  substances  that  are 
alike  in  some  particular  property  or  properties.  This  is 
true  of  the  substances  that  make  up  the  class  we  call 
"  acids,"  as  well  as  of  those  we  call "  bases,"  or  "  alkalies." 
The  word  "  acid  "  means  sour;  sourness  is  a  character- 
istic property  of  most  acids.  The  juices  of  ripe  fruits 

are  sweet  because  they  contain 
sugar;  but  when  they  are  ex- 
posed to  the  air,  the  juices  "  fer- 
ment": their  sugar  is  changed 
to  alcohol  and  carbon  dioxide. 
This  particular  fermentation  is 
due  to  yeast  (cf.  §  129).  The 
change  does  not,  however,  stop 
here.  When  the  fermented 
juices,  which  now  contain  alcohol, 
stand  longer  in  the  air,  they  be- 
come sour,  and  we  have  cider  vinegar,  currant  vinegar, 
wine  vinegar,  etc.  (Fig.  192).  The  cause  of  this  second 
fermentation  is  another  plant,  known  as  the  "  vinegar 
mould,"  or  "  mother  of  vinegar."  The  sourness  of  vinegar 
is  due  to  acetic  acid  (cf.  §  124).  In  a  pure  form  this  is  a 
-colorless,  sharp-smelling  liquid,  which  freezes  at  16°  C., 

188 


FIG.  192. 
Quick  Vinegar  Process. 


CLASSES  OF  ACIDS  189 

and  blisters  the  skin.     Vinegar  usually  has  only  3%  or 
4%  of  it. 

The  materials  present  in  plants  undergo  other  fermenta- 
tions besides  the  one  that  gives  acetic  acid.  Thus,  "Dill  " 
pickles  are  small  cucumbers  fermented  so  as  to  give 
lactic  add;  "  sauer  kraut  "  contains  the  same  acid.  Sweet 
milk  becomes  sour  because  the  milk  sugar  in  it  is  changed 
to  lactic  acid.  Pure  lactic  acid  is  a  thick  liquid  of  very 
sour  taste. 

214.  Classes  of  Acids. —  It  is  not  only  by  fermentation 
of  fruit  juices  that  acids  are  formed.  The  fruits  them- 
selves, as  well  as  other  parts  of  plants,  contain  acids. 
Tomatoes,  cherries,  rhubarb,  etc.,  are  strongly  acid.  Lem- 
ons and  oranges  contain  much  citric  acid;  grape  juice, 
much  tartaric  acid;  apples  contain  malic  acid.  All  of  the 
acids  already  named  in  this  chapter  are  compounds  of 
carbon  with  hydrogen  and  oxygen  (cf.  §  123).  These 
acids  are  called  organic  acids  (cf.  §  3).  There  are  many 
acids  that  contain  no  carbon  at  all,  but  have  some  other 
element  in  place  of  the  carbon.  These  belong  to  the  class 
of  inorganic,  or  mineral,  acids.  Thus,  nitric  acid  contains 
nitrogen,  combined  with  hydrogen  and  oxygen;  sulphuric 
acid  consists  of  sulphur,  hydrogen,  and  oxygen;  phos- 
phoric acid  contains  phosphorus,  hydrogen,  and  oxygen. 
These  three  acids  are  all  thick,  colorless  liquids.  They 
are  commonly  "  diluted  "  with  much  water. 

All  acids  contain  hydrogen,  but  not  all  have  oxygen.  Thus,  hydro- 
chloric acid  (cf.  §  111)  contains  only  hydrogen  and  chlorine.  This  is 
the  acid  of  the  gastric  juice  (cf.  §  364).  The  gastric  juice  of  man  con- 
tains about  0.22  of  1%  of  it;  the  adult  dog  has  several  times  as  much. 


190  ACIDS,  ALKALIES,  AND  CLEANING 

215.  Acids  and  Coloring  Matter. —  Besides  having  the 
property  of  sourness,  acids  have  a  definite  action  on  cer- 
tain coloring  matters,  such  as  purple  cabbage  solution  and 
litmus.    Acids  often  change  the  color  of  the  dyes  in  our 
clothing.    Thus,  "  navy  blue  "  fabrics  are  colored  red  by 
the  common  acids  of  the  laboratory. 

Litmus  is  the  coloring  matter  we  generally  use  in  testing 
for  acids.  It  is  a  blue  substance  obtained  from  certain 
plants  called  lichens  (cf.  §  324).  Either  the  solution,  or 
filter  paper  that  has  been  soaked  in  the  solution,  may  be 
used.  The  prepared  paper  is  called  litmus  paper.  Blue 
litmus  is  changed  to  red  litmus  by  sour  plant  juices  and 
by  other  acids.  A  substance  which  is  able  to  change  blue 
litmus  to  red  is  said  to  have  an  "  acid  reaction." 

216.  Action  of  Acids  with  Metals. —  A  third  important 
property  of  acids  is  that  they  corrode,  or  "  eat,"  metals. 
We  have  learned  that  hydrogen  is  made  by  the  action  of 
some  of  the  acids  upon  zinc,  iron,  etc.  (cf.  §  103).    When 
the  metals  are  so  used,  they  are  "  eaten  up,"  and  disap- 
pear. 

Some  metals,  such  as  copper,  do  not  act  with  dilute 
acids  to  give  hydrogen  (cf.  §  150) ;  but  if  the  metal  and  the 
dilute  acid  are  kept  in  contact  with  air,  the  metal  is 
gradually  corroded.  Here  the  oxygen  of  the  air  acts  with 
the  metal  to  give  the  oxide  of  the  metal  (cf .  §  48) ;  the  oxide 
then  reacts  with  the  acid.  Copper  and  lead  cannot  be 
used  for  cooking  utensils,  because  they  act  with  the  air 
and  the  acids  of  fruits  and  other  food,  producing  poisonous 
compounds. 

Copper  is  "  eaten  "  very  readily  by  dilute  nitric  acid.    If  a  design  is 


ACTION  OF  ACIDS  WITH  CARBONATES  191 

painted  upon  copper  with  asphalt  paint  (Fig.  193),  and  the  copper  is 
put  into  nitric  acid,  the  part  not  covered  by  the  asphalt  is  "  etched  " 
by  the  acid.  When  the  asphalt  is  removed, 
the  design  stands  out  "in  relief." 

217.  Action  of  Acids  with  Carbon- 
ates.— -The  action  of  acids  with  car- 
bonates may  also  be  used  as  a  test 
for  acids.  Marble  (cf.  §  132)  and 
hydrochloric  acid  react  with  much  FIG.  193. 

i  T        •  i       T^13  design  may  be  etched 

effervescence j    because   carbon    dioxide    on  copper  by  dilute  nitric 
escapes   as   a   gas    (cf.  §  126).     The 
other  product  is  calcium  chloride.     It  may  be  obtained  as 
a  white  solid  by  the  evaporation  of  its  solution. 

The  limestone  of  bones,  oyster  and  clam  shells,  and 
of  coral  is  rapidly  eaten  out  by  acids,  and  only  the  animal 
material  is  left.  As  a  result,  bones  that  are  treated  with 
acids  lose  their  stiffening.  The  large  amount  of  acid  in  a 
dog's  stomach  enables  him  to  digest  bone. 

Other  carbonates  react  with  acids  as  marble  and  limestone  do. 
Washing  soda  is  sodium  carbonate,  which  is  made  up  of  sodium,  carbon, 
and  oxygen.  Baking  soda  is  sodium  hydrogen  carbonate,  or  sodium 
bicarbonate  (cf.  §  130).  Both  washing  soda  and  baking  soda  effervesce 
rapidly  when  an  acid  is  added.  The  acid  used  may  be  tomato  juice, 
sour  milk,  or  lemon  juice,  as  well  as  a  mineral  acid  (cf.  §  214).  When 
either  of  the  two  "  sodas  "  is  treated  with  hydrochloric  acid,  there  is 
formed,  besides  water  and  carbon  dioxide,  sodium  chloride,  or  common 
salt  (cf.  §  108).  Soda  was  formerly  rare  and  expensive;  but  it  is  now 
made,  on  an  enormous  scale,  from  common  salt. 

Wood  ashes  contain  potassium  carbonate,  or  "  potash."  The  potash 
is  obtained  from  the  ashes  by  the  use  of  water.  Potash  reacts  with 
hydrochloric  acid  as  soda  does;  but  it  gives  potassium  chloride  instead 
of  sodium  chloride. 


192  ACIDS.  ALKALIES,  AND  CLEANING 

218.  Alkalies,  or  Bases. —  Bases  are  substances  having 
properties  quite  different  from  those  of  acids.    They  turn 
litmus  which  has  been  colored  red  by  acids  back  to  the 
blue  color.    All  substances  that  do  this  are  said  to  have  a 
"  basic  "  reaction.     The  strongest   (most  active)   bases 
are  called  alkalies;  hence  a  basic  reaction  is  also  called 
an  alkaline  reaction. 

The  two  strongest  bases  are  commonly  known  as  lye. 
Better  names  are  sodium  hydroxide  (caustic  soda)  and 
potassium  hydroxide  (caustic  potash).  As  the  chemical 
names  show,  these  substances  are  composed  of  hydrogen 
and  oxygen,  combined  in  the  one  case  with  the  metal 
sodium,  and  in  the  other  with  the  metal  potassium  (cf. 
§  109).  Other  common  bases  are  ammonium  hydroxide 
("ammonia  water'7;  cf.  §  112)  and  calcium  hydroxide 
(slaked  lime).  Calcium  hydroxide  is  the  cheapest  base. 
It  is  made  by  adding  water  to  calcium  oxide  (quicklime). 
Quicklime  is  made  by  heating  limestone  (cf.  §  132). 

Bases  cannot  be  kept  ;f  exposed  to  the  air;  for  they  unite  with  its 
carbon  dioxide  (carbonic  acid;  cf  §  126)  to  form  the  carbonates.  Lime 
that  is  "  air  slaked  "  is  largely  calcium  carbonate.  Solutions  of  potas- 
sium and  sodium  carbonates  have  an  alkaline  reaction,  and  behave 
like  weak  alkalies  in  other  respects,  because  they  react  with  water 
to  form  small  amounts  of  the  hydroxides. 

219.  Caustic  Soda  and  Caustic  Potash. —  When  sodium 
carbonate  (soda)  solution  is  mixed  with  "  milk  of  lime," 
which  is  slaked  lime  "  suspended  "  in  lime  water  (cf.  §  132), 
a  chemical  change  occurs,  and  calcium  carbonate  is  formed 
as  an  insoluble  powder.    The  sodium  hydroxide  (caustic 
soda)  remains  in  solution. 


NEUTRALIZATION;  SALTS  193 

Sodium  carbonate  -f  calcium  hydroxide  give 
(soluble)  (soluble) 

Sodium  hydroxide  +  calcium  carbonate. 

(soluble)  (insoluble) 

The  insoluble  calcium  carbonate  settles,  and  the  solu- 
tion of  sodium  hydroxide  can  be  poured  off.  When  the 
solution  is  evaporated,  the  sodium  hydroxide  remains  as 
a  white  solid.  Potassium  hydroxide  is  made  in  a  similar 
way. 

Both  of  these  solids  are  very  soluble  in  water;  they  even 
attract  water  from  the  air,  becoming  wet,  like  some 
candies.  They  are  changed  back  to  carbonates  by  the 
carbon  dioxide  of  the  air  (cf.  §  218).  Their  water  solutions 
are  "  slimy  "  to  the  touch  (cf.  §  109),  and  act  vigorously 
upon  the  skin,  the  fats,  and  other  organic  matter.  The 
taste  of  a  very  dilute  solution  of  these  "  caustic  alkalies  " 
is  bitter.  Strong  solutions  destroy  the  mucous  membrane 
of  the  mouth  (cf.  §  359)  as  a  hot  body  would.  Hence  the 
name  "  caustic,"  meaning  burning. 

220.  Neutralization;  Salts. —  If  caustic  soda  solution  is 
added  drop  by  drop  to  hydrochloric  acid  containing  lit- 
mus, a  point  is  found  at  which  the  litmus  is  neither  red  nor 
blue,  but  has  a  lavender  color.  If  blue  or  red  litmus  is  put 
into  the  solution,  it  is  either  not  changed  at  all,  or  it  be- 
comes lavender.  We  say  that  the  caustic  soda  has  neu- 
tralized the  acid. 

We  can  neutralize  the  hydrochloric  acid  by  sodium 
carbonate  also;  but  in  this  case  there  is  carbon  dioxide 
given  off.  If  the  neutral  solutions  are  now  evaporated, 
each  will  give  a  residue  of  cubical,  white  crystals.  The 


194  ACIDS,  ALKALIES,  AND  CLEANING 

taste  and  other  properties  of  the  residue  show  that  it  is 
common  salt.  It  is  "  neutral  to  litmus,"  .as  we  should  ex- 
pect from  the  method  by  which  it  was  made. 

If  dilute  nitric  acid  is  neutralized  with  soda  or  with  caustic  soda,  the 
solid  obtained  is  sodium  nitrate;  with  dilute  sulphuric  acid  the  product 
is  sodium  sulphate.  If  potassium  carbonate  or  potassium  hydroxide 
were  used  with  each  of  these  acids,  the  products  would  be  potassium 
chloride,  potassium  nitrate,  and  potassium  sulphate,  respectively.  Since 
all  of  these  substances  are  formed  by  the  neutralization  of  an  acid  by  a 
basic  substance,  just  as  sodium  chloride  is,  they  are  all  called  salts. 
They  have,  in  general,  a  salty  taste,  although  there  are  decided  dif- 
ferences between  the  tastes.  .Calcium  hydroxide,  or  carbonate,  if 
neutralized  with  these  acids,  gives  calcium  chloride,  calcium  nitrate, 
and  calcium  sulphate,  respectively. 

221.  Tests  for  Certain  Salts. —  To  test  for  a  substance, 
as  we  use  the  word  "  test  "  in  this  section,  is  to  find  out 
whether  the  substance  in  question  is  present  or  not.  We 
find  this  by  the  behavior  of  whatever  is  being  tested. 
Thus  we  can  show  that  a  solution  contains  an  acid  by 
using  the  litmus  test,  and  by  the  behavior  of  the  solution 
with  metals,  carbonates,  etc.  (cf.  §§  214  to  217).  Still, 
these  tests  will  not  distinguish  sulphuric  acid  from  many 
other  acids.  But  if  we  apply  the  test  for  sulphates,  in  addi- 
tion to  the  other  tests,  then  there  can  be  no  doubt.  Tests 
"  work  "  because  no  two 'substances  behave  exactly  alike, 
or  have  exactly  the  same  properties  (cf.  §  5). 

In  testing  for  a  salt  we  ask  ourselves  two  distinct  ques- 
tions : — 

(1)  What  metal  does  it  contain? 

(2)  To  what  acid  is  it  related;  that  is,  is  it  a  sulphate,  a 
chloride,  or  what? 


TESTS  FOR  CERTAIN  SALTS          195 

If  a  salt  turns,  out  to  be  a  calcium  salt  and  also  a  car- 
bonate, it  must  be  calcium  carbonate.  If  we  get  a  test  for 
a  sodium  salt,  and  also  for  a  chloride,  the  substance  tested 
must  be  sodium  chloride. 

1.  Chlorides.—  We   test   for   a   chloride    (including   hydrochloric 
acid)  by  dissolving  the  substance  in  distilled  water,  adding  enough 
dilute  nitric  acid  to  give  the  solution  an  acid  reaction  (cf.  §  215),  and 
by  then  adding  a  drop  or  two  of  silver  nitrate  solution.    If  a  chloride 
is  present,  there  will  be  a  white  precipitate  of  silver  chloride,  an  insoluble 
solid.    If  we  shake  up  the  precipitate,  it  will  clot  together.    If  we  pour 
some  of  it  upon  filter  paper,  and  expose  it  to  sunlight,  it  becomes  dark. 
This  last  fact  is  the  basis  of  modern  photography  (cf.  §  188). 

2.  Sulphates. —  We  test  for  sulphates  (including  sulphuric  acid) 
by  adding  to  the  solution  of  the  substance  some  dilute  nitric  acid,  and 
then  a  few  drops  of  a  solution  of  barium  chloride  or  barium  nitrate.    If 
a  sulphate  is  present,  there  will  be  a,  white  precipitate  of  barium  sul- 
phate. 

3.  Nitrates. —  To  test  for  a  nitrate  we  first  make  a  saturated  solution 
of  ferrous  sulphate.    To  about  5  c.c.  of  this  solution,  in  a  test  tube,  we 
add  a  few  drops  of  the  solution  to  be  tested,  and  mix  it,  by  shaking, 
with  the  ferrous  sulphate  solution.   We  then  tilt  the  test  tube,  and  pour 
down  its  side  about  5  c.c.  of  concentrated  sulphuric  acid.    The  heavy 
acid  slides  underneath  the  solution,  and  when  we  hold  the  tube  up-. 
right,  we  find  a  brown  layer  or  ring  between  the  solution  and  the  acid, 
provided  a  nitrate  is  present. 

4.  Carbonates  (either  the  solids  or  their  solutions)  are  tested  for  by 
means  of  dilute  hydrochloric  or  nitric  acid.    Effervescence  takes  place, 
and  we  prove  that  the  escaping  gas  is  carbon  dioxide  by  passing  it 
into  lime  water.    A  white  precipitate  of  calcium  carbonate  is  formed 
(cf.  §126). 

5.  Phosphates. —  We  test  for  phosphates  in  solution  by  adding  to 
the  solution,  first,  a  few  drops  of  concentrated  nitric  acid,  and  then 
a  solution  of  ammonium  molybdate.    A  yellow  solid  is  precipitated,  if 
phosphates  are  present. 

6.  Iron  Salts. —  Solutions  suspected  of  containing  iron  are  treated 


196  ACIDS,  ALKALIES,  AND  CLEANING 

ivith  a  few  drops  of  concentrated  nitric  acid,  and  boiled  for  a  few 
minutes.  Then  a  few  drops  of  a  solution  of  potassium  thiocyanate  or 
.ammonium  thiocyanate  are  added.  A  blood-red  solution  results;  this 
is  pink  if  only  a  little  iron  is  present. 

7.  Sodium  Salts  are  tested  for  by  the  bright,  yellow  flame  they  give 
when  they  are  held,  on  a  platinum  wire,  in  the  colorless  gas  flame  (cf. 
§240). 

8.  Potassium  Salts  give  a  violet  color  to  the  colorless  gas  flame.   The 
•color  is  seen  best  when  it  is  viewed  through  blue  glass;  this  cuts  off  the 
yellow  rays  of  sodium. 

9.  Calcium  Salts. —  We  test  for  a  calcium  salt  by  treating  its  solu- 
tion with  ammonia  water  and  a  solution  of  ammonium  oxalate  (the 
ammonium  salt  of  oxalic  acid).    A  white  precipitate  of  calcium  oxalate 
is  formed.    We  pour  off  the  liquid  portion  from  the  precipitate,  and 
.add  dilute  acetic  acid  to  the  precipitate.    If  the  precipitate  is  really 
•calcium  oxalate,  it  will  not  be  dissolved. 

10.  Ammonium  Salts. —  We  test  for  ammonium  salts  by  adding 
them,  in  solution,  to  a  small  lump  of  quicklime,  or  about  5  c.c.  of  sodium 
hydroxide  solution,  and  warming  the  mixture  gently.    Ammonia  is 
;given  off,  and  can  be  known  by  its  odor. 

222.     Exercises. 

1.  Why  do  we  add  soda  to  tomatoes  in  making  "  cream  tomato  " 
;soup?    How  do  sour  milk  and  soda  "  raise  "  biscuits?    Why  do  straw- 
berries curdle  milk? 

2.  How  could  you  tell  whether  a  soil  was  "  sour  "  or  not? 

3.  Lime  water  is  often  added  to  milk  before  the  milk  is  given  to  a 
child  or  an  invalid;  why? 

4.  "  Galvanized  iron  "  is  iron  covered  with  zinc.   Is  it  a  safe  material 
for  utensils  in  which  fruits  are  cooked?    Why?     Is  "  tinned  "  iron 
.safer?    Why? 

5.  What  base  would  you  use  if  you  wished  to  make  some  potassium 
nitrate  by  neutralization?    What  acid  would  you  use?    How  would 
you  tell  when  you  had  used  just  the  right  amount  of  each? 

6.  In  moist  weather,  laboratory  bottles  sometimes  lose  their  labels. 
If  this  occurred,  how  could  you  tell  whether  a  certain  solid  was,  or  was 


THE  WASHING  OF  CLOTHING  197 

not,   calcium  carbonate?     Ammonium  sulphate?     Sodium  nitrate? 
Iron  chloride? 

223.  The  Washing  of  Clothing. —  We  must  now  apply 
what  we  have  learned  about  acids,  bases,  and  salts  to  some 


FIG.  194. 

Modern  Laundry.  The  illustration  shows  an  electric-power  tub  for  washing ;  one  for  rinsing ; 

a  hot  mangle,  or  ironer;  a  cold  mangle;  electric  irons,  and  laundry  tub.     Courtesy 

of  the  Department  of  Home  Economics,  Cornell  University. 

common  household  practices.    We  begin  with  the  washing 
of  clothing  (Fig.  194). 

Clothing  that  has  been  worn  too  long  has  a  damp, 
sticky  feeling.  It  has  this  feeling  because  its  pores  are 
clogged  with  the  materials  given  off  by  the  skin.  These 
consist  of  perspiration,  of  organic  waste  which  the  body 
casts  off  through  the  skin,  and  of  dead  skin  itself.  When 
these  fill  the  pores  of  clothing,  it  is  unfit  to  wear,  whether 
it  looks  dirty  or  not.  The  evaporation  of  the  perspiration 
regulates  the  temperature  of  the  body  (cf.  §  74),  and  the 
clothing  should  aid,  not  hinder,  this  evaporation.  The 
reason  why  clean  garments  feel  so  comfortable  is  largely 
because  they  have  a  fresh  absorbing  surface. 


198 


ACIDS,  ALKALIES,  AND  CLEANING 


We  should  have  clean  bodies  for  the  same  reason  that  we  should 
wear  clean  clothing,  if  for  no  other;  viz.,  in  order  that  the  pores  of  the 
skin  may  be  permitted  to  act  freely  in  removing  waste,  and  in  evaporat- 
ing the  perspiration. 

The  washing  of  clothing  thus  has  three  objects: 

(1)  To  remove  dirt,  and  to  open  the  pores  of  the  clothing. 

(2)  To  dry  the  washed  clothing,  and  to  give  it  a  new  absorbing 
surface. 

(3)  To  destroy  the  bacteria  which  are  sure  to  accumulate  in  the 
dirt  of  the  skin  and  clothing. 

224.  Soap. —  To  remove  dirt  we  need  not  only  water, 
but  soap.  Soap  is  a  salt,  or  a  mixture  of  salts.  The  metal 

(cf.  §  221)  present  in  hard 
soaps  is  sodium;  in  the  old- 
fashioned  soft  soaps  (Fig. 
195)  it  was  potassium.  The 
acids  to  which  the  soaps  are 
related  (cf.  §  221)  belong  to 
the  class  of  "fatty"  acids,  so 
called  because  they  are  ob- 
tained from  the  fats.  Ex- 
amples of  the  natural  fats 
are  beef  suet,  mutton  tallow, 
and  lard.  Oils  are  liquid 
fats.  Strictly  speaking,  we 
cannot  call  petroleum  products  or  coal-tar  products, 
such  as  kerosene  or  benzene,  oils  at  all.  Palm  oil,  olive 
oil,  and  cotton-seed  oil  are  true  oils.  Soaps  are  made  by 
the  boiling  of  fats  and  oils  with  alkalies. 

When  fat  is  heated  with  sodium  hydroxide,  it  is  "  cut," 
or  "saponified."  Saponify  is  from  the  Latin  sapo  (soap), 
and  means  "  to  make  into  soap."  As  a  result  of  the  boil- 


FIG.  195. 

Old  Way  of  Mnking  Soap  from  Grease 
and  Potash  L.,  e.  Negative  by  T.  B. 
Magath. 


SOAP  199 

ing  with  alkali,  the  fat  disappears  into  solution ;  it  is  changed 
into  the  sodium  salt  (soap)  and  glycerine.  Both  of  these 
are  soluble;  but  when  salt  is  added  to  the  solution  the  soap 
is  "salted  out/'  and  floats  on  top  of  the  solution.  It  is  then 
skimmed  off,  pressed,  and  cut  into  cakes. 


FIG.  196. 

Modern  Way  of  Making  Soap.    The  kettle  is  three  stories  high,  and  holds  perhaps  275,000 
Ibs. :  enough  to  make,  say,  700,000  bars  of  soap.     Courtesy  of  Swift  and  Company. 

In  many  modern  soap  factories  (Fig.  196)  the  fat  is 
first  heated  with  steam.  The  products  are  then  glycerine 
and  the  fatty  acids.  The  soap  is  made  from  the  fatty  acids 
and  sodium  carbonate  (instead  of  the  hydroxide).  Gly- 
cerine is  a  very  valuable  "  by-product  "  of  the  soap  fac- 
tory. 

Until  a  few  decades  ago  soap  was  made  in  the  home.  In  the  spring 
the  winter's  accumulation  of  wood  ashes  was  pounded  down  into  a 
barrel,  and  set  on  a  platform  to  be  "  leached,"  or  extracted  by  water. 
A  hole  was  made  in  the  ashes,  water  was  poured  into  it,  and  the  solu- 


200  ACIDS,  ALKALIES,  AND  CLEANING 

tion  of  potash  that  was  formed  trickled  out  into  little  troughs  in  the 
platform.  The  solution  was  collected  in  kettles,  and  boiled  down  to 
form  the  home-made  lye.  A  kettle  of  fat  was  melted  over  an  open  fire, 
the  lye  was  added  to  this,  and  the  two  were  cooked  together,  often  for 
two  or  three  days.  The  resulting  "  soft  soap  "  was  put  away  in  barrels 
for  the  next  year's  use. 

225.  Action  of  Soap. —  When  a  sodium  soap  is  dis- 
solved, it  is  partly  broken  up,  by  the  action  of  the  water, 
into  sodium  hydroxide  and  the  fatty  acids  (cf.  §  218). 
The  sodium  hydroxide  acts  upon  the  fats  and  oils  of  the 
skin  and  clothing,  and  partly  converts  them  into  soaps, 
so  that  they  also  are  dissolved  by  the  water.    In  using 
soap  we  are  using  lye  in  a  most  convenient  form,  for  its 
caustic  properties  are  so  altered  that  it  can  cleanse  fabrics 
and  the  skin  without  injuring  them.     Toilet  soaps  are 
"  neutral  to  litmus,"  because  an  excess  of  fat  is  used,  so 
that  the  amount  of  free  alkali  is  small.     Laundry  soaps 
have  more  free  alkali. 

Soap  has  not  only  this  chemical  action,  but  the  lather, 
or  suds,  acts  mechanically,  entangling  the  undissolved  fat, 
dead  skin,  and  dirt,  and  removing  them. 

226.  Soap  and  Hard  Water. —  We  have  already  learned 
(cf.  §  82)  that  the  hardness  of  water  is  its  soap-consuming 
power.     Hardness  is  due  to  dissolved  salts,  especially 
calcium    carbonate    (limestone)    and    calcium    sulphate 
(gypsum).    When  soap  is  put  into  a  hard  water,  it  acts 
with  these  salts,  forming  the  calcium  salts  of  the  fatty 
acids.    These  are  insoluble,  and  separate  as  a  scum,  called 
lime  soap.    If  soap  is  used  in  sufficient  amount,  it  will 
soften  such  a  water;  but  soap  is  too  expensive.    Besides, 


MATERIALS  OF  CLOTHING  201 

the  lime  soap  gets  into  the  pores  of  the  fabric,  and  in- 
jures it. 

If  a  soft  water  cannot  be  obtained  in  any  other  way,  a  method  of 
"  softening  "  should  be  used.  To  remove  permanent  hardness  from  a 
laundry  water  we  often  use  soda  or  borax.  Borax  is  sodium  borate. 

Sodium  carbonate  (or  borate) + calcium  sulphate  give 
(soluble)  (soluble) 

sodium  sulphate + calcium  carbonate  (or  borate). 

(soluble)  (insoluble) 

The  sodium  sulphate  left  in  the  solution  has  no  action  with  the  soap. 
Both  temporary  and  permanent  hardness  may  be  removed  at  one  opera- 
tion by  the  correct  amount  of  ammonia  water  or  caustic  soda. 

Washing  powders  also  precipitate  hardness.  They  are  usually  soda 
or  potash,  or  dried  soap  containing  an  excess  of  alkali. 

227.  Materials  of  Clothing. —  Two  common  vegetable 
fibers  used  for  clothing  and  in  the  household  are  cotton 
and  linen.  Cotton  is  the  covering  of  the  seed  of  the  cotton 
plant;  while  linen  is  found  in  the  stalks  of  flax.  Both  are 
chiefly  cellulose  (cf.  §  123). 

Although  cotton  and  linen  are  much  alike  chemically, 
they  are  very  different  physically.  Both  consist  of  hollow 
tubes  (Fig.  197);  but  the  fibers  of  cotton  are  flat  and 
twisted,  while  those  of  linen  are  nearly  straight,  and  have 
thick  walls  with  a  central  opening. 
Linen  cloth  is  stronger  than  cotton, 
but  cotton  is  lighter  and  more  elastic. 

Cotton  and  linen   are  easily  de- 
stroyed by  mineral  acids  (cf.  §  214),  Woo(     - 
if  these  are  strong  or  are  allowed  to     Fiberg  /'^  Linen 
dry  upon  the  fabric.     They  are  not      ±erin°golof thewooi! scaly 


202  ACIDS,  ALKALIES,  AND  CLEANING 

so  easily  harmed  by  alkalies.  In  fact,  if  cotton  is  treated 
with  strong  alkali  for  a  short  time,  and  is  then  washed 
thoroughly,  it  is  actually  made  stronger,  and  has  a  glossy, 
silky  appearance.  Cotton  so  treated  is  called  mercer- 
ized cotton. 

Wool  and  silk  (Fig.  198)  are  of  animal  origin,  and  con- 
sist not  only  of  carbon,  hydrogen,  and  oxygen,  as  cellulose 
does,  but  contain  nitrogen  also  (cf.  § 
123).    They  are  the  opposites  of  cotton 
and   linen    in    chemical    behavior;    for 
they   are  not  readily   acted   upon  by 
acids,    but    are    easily    destroyed    by 
FIG.  IDS.  alkalies.    The  fibers  of  wool  are  entirely 

Cotch°e0siik"orm.ibers  °f  different  from  those  of  linen  and  cotton. 
Instead  of  consisting  of  long  cells,  wool 
is  made  up  of  short,  thick  cells,  with  the  projecting  edges 
of  each  lapping  over  part  of  the  one  next  to  it  (Fig.  197). 
The  surface  thus  appears  to  be  covered  with  horny  scales 
all  lying  in  one  direction.  No  method  of  washing  wool 
should  be  used  that  will  force  the  cells  closer  together, 
or  the  wool  will  shrink,  and  finally  become  stiff  and 
board-like. 

228.  Dyes. —  Dyes  are  colored  compounds  that  are 
either  absorbed  by  the  pores  of  a  fiber,  or  combine  chemi- 
cally with  the  fiber  to  form  a  colored,  insoluble  compound. 
Silk  and  wool  are  much  more  active  chemically  than  cotton 
and  linen.  Hence  silk  and  wool  can  combine  directly 
with  many  more  dyes.  We  can  think  of  the  process  of 
dyeing  cloth  as  a  reaction  much  like  that  which  occurs 
when  an  acid  and  a  base  unite  to  form  a  salt  (cf.  §  220). 


PAINTS  203 

Since  cellulose  combines  with  very  few  dyes  directly,  it  and  the 
dye  must  be  held  together  by  a  third  substance,  which  can  unite  with 
the  cellulose  on  the  one  hand,  and  with  the  dye  on  the  other.  Such 
a  substance  is  called  a  mordant.  Here,  also,  we  can  look  upon  the 
dyeing  process  as  a  reaction  between  acids  and  bases;  only  there  are 
three  substances  in  the  reaction  instead  of  two.  The  final,  complex  salt 
is  the  dyed  fabric  itself. 

Aluminum  hydroxide  is  a  common  mordant.  It  is  insoluble,  and  it 
is  sticky,  like  boiled  starch.  It  is  formed  in  the  fibers  of  cloth  when  we 
soak  the  cloth  in  aluminum  acetate,  and  then  in  ammonia  water.  In  the 
making  of  calico  the  pattern  is  first  printed  on  cotton  cloth  with  a 
mordant,  and  the  cloth  is  then  soaked  in  a  dissolved  dye.  Tne  dye  com- 
bines with  the  mordant,  but  not  with  the  cloth  alone.  The  uncom- 
bined  dye  is  washed  out.  If  different  parts  of  a  pattern  are  printed 
with  different  mordants,  a  number  of  colors  can  be  made  from 
the  same  dye. 


229.  Paints. —  Common  paint  consists  of  linseed  (flax 
seed)  oil  and  turpentine,  mixed  with  "  white  lead,"  or 
"  zinc  white/'  and  a  pigment  to  give  color.  White  lead, 
etc.,  are  compounds  used  to  give  the  paint  "  body  "  or 
"covering  power."  The  turpentine  not  only  thins  the 
paint,  but  assists  in  drying  the  oil. 

When  paint  dries,  its  linseed  oil  is  oxidized  by  the  air  to 
a  hard  gum.  Considerable  heat  is  given  off  in  the  process; 
hence  heaps  of  cloths  containing  paint  or  linseed  oil  often 
take  fire  without  an  apparent  cause  ("  spontaneous  com- 
bustion ").  Such  cloths  should  never  be  left  about  a 
building  except  in  covered  metal  boxes. 

To  remove  a  paint  stain  from  a  fabric  we  need  usually 
remove  only  the  linseed  oil.  This  is  soluble  in  benzine, 
gasoline,  etc.  When  we  have  removed  the  oil,  we  can 
generally  remove  the  white  lead  by  brushing  or  rubbing. 


204  ACIDS,  ALKALIES,  AND  CLEANING 

When  we  use  gasoline  as  a  cleaning  agent,  we  should 
take  great  care  to  remain  away  from  a  fire.  Especially 
should  we  use  care  in  rubbing  silk  that  is  wet  with  gaso- 
line, lest  the  gasoline  may  be  set  on  fire. 

230.  Removal  of  Stains. —  When  we  wish  to  remove  a  stain  from  a 
fabric,  we  should  consider  whether  the  substance  causing  the  stain 
must  be  changed  chemically,  or  whether  it  can  be  removed  by  physical 
means.  Thus,  paraffin  ("  white  wax  "),  the  material  of  many  candles, 
especially  of  colored  candles,  is  not  a  fat,  and  cannot  be  saponified  by 
lye  and  soap.  It  is,  however,  readily  dissolved  by  benzine,  gasoline, 
or  ether,  and  can  thus  be  removed.  An  excellent  way  is  to  wet  the 
paraffin  spot  with  benzine,  and  then  to  press  it,  by  means  of  a  flat  iron, 
between  blotters. 

Milk  and  cream  stains,  if  fresh,  are  washed  out  with  cold  water.  If, 
however,  they  are  old  stains,  the  water  of  the  milk  will  have  evaporated, 
leaving  the  fat  in  the  fiber.  To  remove  them  we  use  soap  and  water, 
or  ammonia  water,  or  we  moisten  the  spot  with  benzine  and  press  it 
between  blotters.  Ammonia  water,  like  soap  and  lye,  saponifies  the 
fat  and  makes  it  soluble. 

Iron  rust  must  be  removed  by  chemical  means.  It  is  a  base  (ferric 
oxide  or  hydroxide) ;  hence  we  use  an  acid  to  remove  it.  Dilute  hydro- 
chloric acid  (cf.  §  111),  lemon  juice  and  salt,  etc.,  are  commonly  used. 
The  acid  must  then  be  rinsed  out  and  neutralized. 

Ink  stains  are  often  hard  to  remove,  because  we  cannot  be  sure  of 
what  the  ink  is  made.  Fresh  ink  stains  are  usually  taken  out  by  fresh 
milk.  Old  stains  are  soaked  in  water,  and  treated  with  oxalic  acid 
(10%  solution).  The  acid  is  a  poison.  It  should  finally  be  rinsed  out 
with  water,  and  neutralized  by  a  mild  base  like  borax  or  ammonia 
water. 

Old-fashioned  inks  contained  iron  compounds;  hence  stains  caused 
by  them  are  treated  like  iron  rust. 

We  must  remember  that  most  active  chemicals,  such  as  acids  and 
bases,  affect  dyes  (cf.  §  215);  hence  they  can  rarely  be  used  to  remove 
stains  from  colored  fabrics.  The  cleaning  agent  should  be  used  with  a 
piece  of  the  goods,  before  it  is  applied  to  the  garment.  Acids  spilled 


EXERCISES  205 

on  cloth  should  be  washed  out  at  once  with  water,  and  the  spots  treated 
with  a  solution  of  baking  soda,  borax,  etc.  Ammonia  should  rarely 
be  used  to  neutralize  acid  spots  on  colored  goods;  it  may  react  with  the 
dye,  as  well  as  with  the  acid  we  wish  to  neutralize. 

231.  Summary. —  Acids  are  the  sour  substances  present  in  fruit, 
vinegar,  pickles,  etc.    They  are  either  organic  or  inorganic.    Inorganic 
acids  are  also  called  mineral  acids. 

Acids  act  upon  coloring  matter,  metals,  carbonates  of  metals,  bases, 
and  fabrics,  especially  upon  cotton  and  linen. 

Alkalies  are  the  strongest  bases.  They  turn  litmus  blue,  destroy 
skin  and  flesh,  saponify  fats,  neutralize  acids,  and  destroy  fabrics, 
especially  wool  and  silk. 

Neutralization  is  the  chemical  action  between  an  acid  and  a  base. 
After  neutralization  the  solution  contains  a  salt. 

Testing  for  salts  consists  in  finding  the  metal  present  in  them,  and 
the  acid  to  which  they  are  related. 

Washing  of  clothing  is  for  the  purpose  of  removing  dirt,  opening  the 
pores  of  the  cloth,  and  destroying  bacteria. 

Soap  is  the  sodium  salt  of  certain  fatty  acids;  it  is  made  by  the  boil- 
ing of  alkalies  with  fat,  and  is  soluble  in  water. 

Soft  water  and  soap  give  alkali  and  organic  acid  in  mild  form.  Hard 
water  first  gives  a  lime-soap  scum.  Hard  water  is  "  softened  "  by  soap, 
soda,  borax,  ammonia  water,  etc. 

Cotton  and  linen  consist  of  long  hollow  fibers  of  cellulose. 

Wool  consists  of  short,  thick  cells  having  overlapping  scales. 

Silk  and  wool  can  be  dyed  directly  more  easily  than  cotton  and  linen. 

Mordants  are  substances  used  to  unite  the  dye  to  the  fabric. 

Paint  generally  consists  of  linseed  oil,  turpentine,  a  pigment,  and 
lead  white,  or  some  other  substance  with  "covering"  power. 

Stains  are  removed  sometimes  by  physical,  and  sometimes  by 
chemical  means. 

232.  Exercises. 

1.  If  you  have  spilled  dilute  hydrochloric  acid  upon  woolen  cloth- 
ing, what  should  you  use  to  neutralize  the  acid  and  to  restore  the  color? 
Would  caustic  soda  do?  Why? 


206  ACIDS,  ALKALIES,  AND  CLEANING 

2.  Why  is  it  not  enough  to  wash  clothing  in  cold  water,  even  with 
soap?    Why  is  not  enough  to  use  hot  water,  without  soap? 

3.  Commercial  laundries  sometimes  use  acids,  such  as  hydrochloric 
acid,  for  the  washing  of  clothing;  why  is  this  not  a  good  practice? 
What  fabrics  especially  are  injured? 

4.  Why  should  wool  be  washed  with  mild  soaps,  and  in  warm,  but 
not  hot,  water? 

5.  How  could  you  test  a  soap  for  an  excess  of  alkali? 

6.  Why  does  not  a  soap  give  a  lather  as  quickly  in  well  water  as  in 
rain  water? 

7.  Why  is  " blueing"  used  in  the  laundering  of  white  goods? 

8.  Why  do  not  men  make  soap  out  of  petroleum  and  lye? 

9.  Why  should  oily  cloths  piled  in  a  heap  take  fire  spontaneously, 
while  if  outspread  they  do  not? 

10.  What  causes  the  "scum"  that  forms  on  the  surface  of  an  open 
can  of  paint?    Gasoline  and  benzine  are  cheaper  than  turpentine;  are 
they  good  substitutes  for  it?    Why? 


CHAPTER  XII 

WATER,  HEAT,  AIR,  AND  LIGHT  IN  THE  HOUSE 

233.  Modern    Conveniences. —  In    no    respect    does 
modern  life  differ  more  greatly  from  that  of  the  past 
than  in  home  comforts  and  conveniences.     Ancient  and 
medieval    peoples   built   larger   monuments,    and   more 
enduring  tombs  and  temples,  than  we  are  building;  but 
the  homes  of  the  people  were  cheerless  indeed  when 
compared  with  those  of  American  cities  to-day.    Even  the 
wealthy  could  not  always  have  heat,  light,  and  water 
in  abundance;  consequently  the  winter  was  full  of  dis- 
comfort, houses  were  insanitary  and  dark,  and  filth  and 
dirt  were  everywhere  the  rule.     The  cleanliness,  light, 
and  warmth  of  our  houses,  schools,  and  public  buildings 
are  due  to  modern  scientific  discoveries  and  their  appli- 
cation. 

234.  Water  in  House  and  Town. —  We  have  already 
considered  the  need  of  pure  water  (cf.  §§  81  to  85,  and 
226) ;  we  must  also  remember  that  modern  man  needs  an 
abundance  of  water.     In  our  houses  we  need  it  for  drink- 
ing, for  cooking,  and,  as  ice,  for  preserving  food ;  for  bath- 
ing the  body,   washing  dishes   and   clothing,   spraying 
lawns  and  gardens,  and  carrying  waste  matter  into  the 
sewage  system.     The  industries  of  the  city  need  it  for 
producing  steam,  for  washing  and  rinsing  on  a  large  scale, 

207 


208        WATER,  HEAT,  AIR,  AND  LIGHT  IN  THE  HOUSE 


as  in  laundries,  tanneries,  slaughter  houses,  starch  fac- 
tories, sugar  refineries,  gas  works,  petroleum  refineries, 
dye  works,  paper  mills,  etc.  The  community  as  a  whole 
needs  it  for  protection  against  fire,  and  to  carry  away  its 
sewage. 

Some  cities  pump  water  into  "standpipes,"  or  elevated 
reservoirs,  from  which  it  flows,  under  pressure,  into  the 
street  "  mains,"  and  then  into  the  houses;  others  use 
force  pumps  of  large  capacity  (cf.  §  42)  ;  others,  still,  have  a 
combination  of  both  systems,  using  the  reservoirs  to  assist 
the  pumps  when  there  is  the  greatest  demand  for  water, 
as  at  meal-cooking  time,  or  when  there  is  a  serious  fire. 

In  order  to  get  enough  water,  great  cities  go  to  enormous  expense. 
The  Romans  built  great  aqueducts  (Fig.  199)  to  bring  water  from  the 

lakes  of  the  Apennines  to 
Rome.  New  York  City  now 
gets  its  water,  through  an 
aqueduct,  from  the  Catskills, 
90  miles  away.  Denver  is 
fortunate  enough  to  be  sur- 
rounded by  mountains  having 
many  streams  of  pure  water; 
this  is  allowed  to  flow  through 
pipes,  by  gravity,  to  the  city. 
Los  Angeles  gets  its  water 
,  from  mountains  many  miles 

How  water  may  be  carried  under  a  river. 

away.     The  cities  on  or  near 

the  Great  Lakes  use  lake  water;  but  they  take  great  care  to  prevent 
the  sewage  from  the  city  from  polluting  the  water  intended  for  the 
city.  Chicago  has  built  an  expensive  "  Drainage  Canal"  to  carry 
water  from  Lake  Michigan  into  the  Illinois  River,  and  thus  to  empty 
the  city's  sewage  into  the  Mississippi  instead  of  into  the  lake  system. 
Inland  cities  usually  get  their  water  supply  from  a  near-by  stream; 
but  such  water  needs  careful  filtration. 


199 


HYDRANTS  AND    TRAPS  209* 

235.  Plumbing. —  In  some  cities  water  is  sold  to  con- 
sumers at  a  "flat  rate/7  without  regard  to  the  amount 
used.     Other  cities  use  a  meter,  or  measuring  device,, 
which  records  the  amount  that  actually  flows  from  the 
street  mains  into  the  house.     The  pipes,  faucets,  traps, 
etc.,  through  which  water  is  carried  to  the  different  parts 
of  the  house,  or  away  from  it,  make  up  the  plumbing  of 
the  house.     The  word  "plumbing"   is  from  plumbum, 
Latin  for  "lead."     To  make  lead  pipes,  men  force  hot 
lead,   under  great  pressure,   through  steel  dies  having 
ring-shaped  openings.     Nowadays   iron   pipes,    as    well 
as  lead  ones,  are  used  for  plumbing.     The  iron  is  "  gal- 
vanized" to  prevent  rusting  (cf.  §  222,  Ex.  4). 

Lead  is  used  for  pipes,  sink  linings,  etc.,  because  it  is 
not  rusted  readily  (cf.  §  216).  Lead  pipes  .are  also  easy 
to  bend  around  corners  and  into  special  shapes.  Then, 
too,  they  can  be  cut  readily  where  necessary,  and  the 
pieces  joined  by  solder. 

But  the  use  of  lead  has  one  disadvantage,  in  that  the  fresh  surface 
of  the  metal  is  acted  upon,  and  dissolved,  by  water.  When  lead  is 
taken  regularly  into  the  body,  as  in  drinking  water,  it  accumulates  until 
it  causes  sickness.  Painters  often  have  "painters'  colic"  because  of 
the  lead  compounds  in  paint  (cf.  §  229) .  Lead  is  not  acted  upon  greatly 
by  pure  water;  but  air  and  soft  water,  especially  if  carbon  dioxide  is 
present  (cf.  §  80,  table),  gradually  " dissolve"  it.  Hard  water  acts. 
upon  the  inside  of  the  pipe  after  a  time,  and  produces  a  coating  that 
does  not  dissolve.  This  protects  the  lead  and  the  water.  We  should 
always  let  water  run  for  a  moment  from  a  new  lead  pipe,  so  as  to  make 
sure  that  the  water  we  drink  is  free  from  lead  compounds. 

236.  Hydrants  and  Traps. —  Faucets,  or  hydrants,  are  usually  of 
brass,  sometimes  plated  with  nickel.     They  are  generally  of  two  kinds: 

(1)  Those  having  a  movable,  tapered  plug  with  a  hole  in  it. 


210        WATER,  HEAT,  AIR,  AND  LIGHT  IN  THE  HOUSE 

(2)  Those  in  which  the  opening  is  closed  by  a  rubber  "  plunger,"  or 
"gasket." 

Waste  water,  like  that  from  a  sink  or  bowl,  is  discharged  into  the 
sewer  pipe  through  a  trap  (Fig.  200).  This  is  a  bend  in  the  pipe, 
which  remains  full  of  water,  and  cuts  off  connection  between  the  air  of 
the  room  and  that  of  the  sewer.  Water  should  be 
-From  sink  run  every  few  days  into  sinks  and  floor  drains  that 
are  little  used,  so  that  the  traps  may  always  be  full. 

237.  Kindling  a  Fire. —  The  discovery 
Drain  Plug  of  fire  came  long  before  the  dawn  of  history. 

To  Waste  Pipe j.  ...  , 

Fig  200.  Many  primitive  peoples  still  start  their 


A  Trap.  fij.es  ^y  rukkmg  one  piece  of  wood  against 

another.  The  friction  gives  the  temperature  needed  to 
set  on  fire  the  bits  of  bark,  pitch,  dry  fungus,  etc.,  that 
serve  as  tinder  (cf.  Fig.  63,  §  76).  A  century  ago  the 
kindling  method  used  in  Europe  and  America  was  to 
strike  steel  or  iron  pyrites  (a  compound  of  iron  and  sul- 
phur) against  flint.  In  the  flintlock  musket  this  method 
was  used  to  kindle  gunpowder. 

The  first  practical  friction  matches  were  made  about 
1827.  They  consisted  of  wooden  splints  partly  coated 
with  sulphur,  and  tipped  with  potassium  chlorate,  anti- 
mony sulphide,  and  gum.  Friction  against  a  rough  sur- 
face produced  heat  enough  to  make  the  sulphur  unite 
with  the  oxygen  of  the  potassium  chlorate,  and  the  heat 
of  the  burning  sulphur  set  the  wooden  splint  on  fire.  The 
"parlor"  match  has  a  tip  containing  paraffin  or  sulphur, 
yellow  phosphorus,  and  some  oxidizing  substance  like 
potassium  chlorate  or  "red  lead."  Glue  is  used  to  make 
all  the  substances  adhere  to  the  wood. 

Parlor  matches  are  ignited  much  more  easily  than 


THE  FIREPLACE  211 

sulphur  matches;  in  fact,  they  often  cause  accidental  fires. 
Another  serious  trouble  with  the  parlor  match  is  that  it 
is  deadly  to  the  workmen  (and  these  are  largely  women 
and  children)  who  handle  it.  They  are  frequently  at- 
tacked by  a  dreadful  disease  called  "phossy  jaw."  For 
these  reasons  many  governments  forbid  the  use  of  parlor 
matches. 

Safety  matches  are  less  convenient  to  use  than  other  forms,  because 
they  must  be  struck  against  the  surface  of  the  box;  but  they  are  not  so 
likely  to  take  fire,  and  are  much  less  dangerous  to  make.  The  reason 
for  this  is  that  safety  matches  use  red  phosphorus,  instead  of  the  more 
active  yellow  form,  and  that  the  phosphorus  is  on  the  striking  surface 
instead  of  on  the  splint  itself.  The  striking  surface  is  red  phosphorus 
and  sand;  the  tip  contains  antimony  sulphide,  some  oxidizing  substance, 
and  glue.  A  " strike  anywhere"  match  is  now  being  made  with  phos- 
phorus sulphide,  a  substance  that  does  not  cause  the  evil  effects  of 
yellow  phosphorus. 

238.  The  Fireplace. —  It  is  hard  for  us  to  realize  that 
modern  methods  of  heating  are  of  such  recent  origin  that 
our  grandparents,  or  certainly  our  great-grandparents, 
lived  at  a  time  when  all  of  these  methods  were  little 
known,  and  when  the  heating  and  much  of  the  lighting 
of  the  house  was  done  by  the  open  fireplace  (Fig.  201). 
No  modern  method  of  heating  brings  into  the  house  the 
cheer  and  sentiment  that  belonged  to  the  fireplace;  hence 
men  try,  whenever  possible,  to  use  it  as  an  ornament,  no 
matter  what  system  they  use  for  the  actual  heating.  But 
the  fireplace  is  more  than  an  ornament,  for  it  is  one  of 
the  best  means  of  ventilation  (cf.  §  248),  carrying  out  the 
foul,  cooled,  lower  air,  and  making  room  for  the  warmed, 
fresh  air  that  is  so  much  needed  for  health  and  comfort. 

The  accessories  of  the  fireplace  were  numerous.     The  necessary 


212        WATER,  HEAT,  AIR,  AND  LIGHT  IN  THE  HOUSE 

ones  were  the  crane,  a  swinging  frame  from  which  the  cooking  utensils 
were  hung,  and  the  andirons,  or  "dogs,"  used  to  hold  the  fuel  up  from 
the  hearth,  so  that  the  air  might  have  better  access.  In  large  fireplaces 
a  huge  "backlog"  was  used.  This  was  placed  at  the  back  of  the  fire, 
while  smaller  pieces  of  fuel  were  laid  on  the  andirons,  before  it.  The 


Fig.  201. 
The  Fireplace  of  a  Modern  Living  Room. 

backlog  often  lasted  for  days,  and  from  it  the  new  fire  was  built  in  the 
morning. 

239.  Stoves. —  In  a  stove  the  heat  produced  by  burn- 
ing fuel  can  be  used  in  a  more  economical  and  convenient 
way  than  in  the  fireplace.  Stoves  are  usually  of  cast  iron 
or  steel.  The  best  surfaces  for  absorbing  and  radiating 
heat  are  not  highly  polished  and  plated,  but  roughened 
and  black  (cf.  §  181).  In  a  cooking  stove  both  the  top 
and  the  oven  must  be  heated.  To  heat  the  oven  evenly, 
we  rieed  specially  constructed  flues,  or  outlets.  If  the 
h'ot  gases  formed  in  burning  are  allowed  to  escape  at  once, 


GASOLINE  AND  KEROSENE  STOVES  213 

there  is  great  waste  of  fuel;  for  only  the  top  of  the  stove 
is  heated.  But  the  cook  stove  has  a  "back  damper" 
which  compels  these  gases  to  travel  in  a  roundabout  way, 
heating  a  large  surface  of  the  oven  before  they  enter  the 
pipe  leading  to  the  chimney.  Wood  and  coal  stoves  have 
a  slightly  different  construction. 

240.  Gas  Stoves. —  Gas  stoves  are  rapidly  taking  the 
place  of  wood  and  coal  stoves,  wherever  gas  can  be  ob- 
tained.    The  gas  used  for  lighting  has  a  smoky  flame, 
and  deposits  soot.     To  avoid  the  soot,  and  to  secure  a 
hot  flame,  we  use  the  principle  of  the  Bunsen 

burner  (Fig.  202).  In  this  burner  the  gas 
escapes  through  a  pin-hole  into  a  mixing  tube. 
The  tube  has  air  holes  near  the  gas  inlet.  The 
small,  rapid  current  of  gas  draws  the  air  into 

these  air  holes,  and  the  mixture  of  air  and  gas     

burns  at  the  top  of  the  burner.     The  flame  is       Fig.  202. 
smaller  than  if  the  gas  were  burned  directly; 
but  it  is  also  hotter.     Since  the  gas  is  mixed  thoroughly 
with  air,  the  flame  is  smokeless.     Smoke,  or  soot,  repre- 
sents wasted  fuel. 

If  the  supply  of  air  taken  in  by  the  Bunsen  burner  is 
too  great  for  the  amount  of  gas,  there  is  a  slight  explosion 
in  the  mixing  tube,  and  the  flame  "strikes  back"  to  the 
narrow  opening  inside  the  burner.  If  we  regulate  the 
gas  supply  and  the  size  of  the  air  holes,  this  will  rarely 
take  place.  In  gas  stoves  the  air  holes  are  at  the  front, 
near  the  openings  through  which  gas  enters. 

241.  Gasoline  and  Kerosene   Stoves. —  The  gasoline 
burner  is  essentially  a  Bunsen  burner.     To  light   the 


214        WATER,  HEAT,  AIR,  AND  LIGHT  IN  THE  HOUSE 

gasoline  stove  we  run  some  of  the  gasoline  into  a  "cup," 
and  there  burn  it  to  heat  the  vaporizer.  When  the 
vaporizer  is  hot,  we  allow  the  liquid  gasoline  to  enter  it 
very  slowly ;  it  is  there  changed  to  the  gaseous  form.  Air 
is  drawn  into  the  burner  by  the  current  of  gasoline  vapor, 
and  the  mixture  burns  at  the  top  of  the  burner  with  a 
very  hot  flame,  as  in  the  case  of  gas. 

The  use  of  gasoline  is  attended  with  some  danger  unless  the  stove  is 
of  good  construction,  and  unless  great  care  is  taken  in  handling  it. 
People  think  of  gasoline  as  a  liquid.  They  should  rather  think  of  it  as 
a  gas.  It  boils  very  low  (60°  to  70°  C.),  and  what  seems  to  be  only  a 
little  of  the  liquid  may  give  a  great  deal  of  the  vapor.  The  vapor 
forms  a  very  explosive  mixture  with  air.  Reservoirs  should  not  be 
filled  when  fires  are  anywhere  about,  and  if  any  gasoline  is  spilled, 
the  room  should  be  thoroughly  aired  before  a  burning  body  is  brought 
into  it. 

Kerosene  burns  with  a  smoky  flame,  and  has  a  high  boiling  point 
(150°-250°C.;  cf.  §  121);  hence  burners  using  it  must  have  hotter 
vaporizers  and  a  greater  air  supply  than  gasoline  burners. 

242.  Electric  Stoves  and  Heaters. —  The  great  advan- 
tage of  electric  heating  is  leading  to  its  use  on  a  con- 
stantly larger  .scale   (cf.   §   157).     The  electric  flat-iron 
(Fig.  194,  §  223)  requires  no  hot  range  to  heat  it,  nor  any 
particular  room  for  its  use,  but  may  be  used  wherever 
there  is  an  electric  "outlet."     The  electric  stove  needs  no 
flue,  and  heats  without  fuel  or  odor.     The  electric  heating 
pad  is  far  superior  to  the  hot-water  bag,  for  it  does  not 
grow  cold.     But  electric  heating  appliances,  like  all  others, 
require  care;  if  overheating  occurs  in  the  circuit,  there  is 
serious  danger  of  fire  (cf.  §  258). 

243.  Hot  Water  and  Steam  Heating.— The  hot-air 
furnace  has  been  described  already  (cf.  §  67).     It  brings 


THERMOSTAT 


215 


Overflow  Pipe- 


warm  air  into  the  house,  because  it  sets  up  convection 

currents.     Hot-water  heating  systems  (Fig.  203)  depend 

upon   the   convection   currents    set    up    in    cold   water 

when    one   part   of    the 

water    is    heated.      The 

heating    is    done    in    a 

furnace,  and   the   water 

heated,  being  lighter  than 

the  colder  water  in  the 

pipes  and  radiators,  rises 

to  take  its  place.     The 

cooler  water  flows  back 

to    the    furnace,    to    be 

heated.     A  "standpipe" 

in    the   attic    keeps    the 

radiators  full  of  water. 

In  steam  heating,  a  furnace 
is  used  to  convert  water  into 
steam,  and  the  heat  given  off 
by  the  steam,  as  it  cools  and 
condenses  (cf.  §  89),  warms 

the  house.     The  hot  water  remaining  after  condensation  returns  to 
the  boiler  to  be  reconverted  into  steam. 

244.  Thermostat. —  We  have  already  learned  that  a 
thermometer  tells  us  temperature  by  registering  the 
difference  in  expansion  between  mercury  and  glass  (cf. 
§  62).  We  could  also  make  a  thermometer  out  of  two 
metals  that  expand  different  amounts  when  heated 
through  the  same  degrees  of  temperature.  Thus,  we  can 
rivet  together  a  small  bar  of  iron  and  one  of  brass  so  that 
the  resulting  compound  bar  is  straight  when  cold ;  but  when 


Fig.  203. 
Hot  Water  Heating  System. 


216        WATER,  HEAT,  AIR,  AND  LIGHT  IN  THE  HOUSE 


the  bar  is  heated,  the  unequal  expansion  of  the  two  metals 
will  produce  a  curved  bar.  If  we  fasten  one  end  of  the 
compound  bar,  leaving  the  other  end  free,  the  free  end 
will  be  able  to  push  against  a  pointer,  and  so  to  record  the 
temperature. 

In  the  thermostat  (Fig.  204),  an  instrument  used  to 
regulate  the  temperature  of  a  room,  the  bar  is  made  a 
part  of  two  electric  circuits;  it  will  permit 
the  current  to  flow  in  one  circuit  when  the 
room  becomes  too  warm,  and  through  the 
other  circuit  when  the  room  becomes  too 
cold.  Electromagnets  in  the  two  circuits 
control  the  supply  of  steam,  hot  water,  etc., 
turning  it  on  or  off  as  needed. 

245.  Exercises. 

1.  What  is  the  source  of  the  water  in  the  city  in 
which  you  live?     Is  the  water  hard  or  soft?     Is  it 
purified  in  any  way  before  it  enters  the  mains?     How 
large  are  the  mains?     Is  your  city  water  ever  tested 
for  impurities?     What  have  been  the  results  of  the 
tests  for  the  last  two  months?     How  much  does  your 
family  pay  for  water?    How  many  cubic  feet  of  water 
does  your  family  use  in  a  month  or  in  a  quarter? 
2.    What  is  the  form  of  the  plumbing  "  traps  "  in  your  house?    Are 
they  like  the  trap  shown  in  Fig.  200?     If  your  basement  or  barn  has  a 
floor  drain,  find  out  the  form  of  the  trap,  and  describe  it. 

3.  How  are  the  outside  faucets  of  your  house  emptied  to  prevent 
the  water  in  them  from  freezing  in  winter?    Why  not  let  the  water 
freeze  in  them? 

4.  Suggest  some  ways  of  kindling  fire  without  the  use  of  friction. 

5.  Show  that  the  wood  and  coal  cook  stove  is  really  an  improved 
form  of  fireplace.     Show  that  the  fireplace  fire  is  an  improved  form  of 
the  open  fire  built  against  a  rock. 


Fig.  204. 

Thermostat.  I  f 
the  room  be- 
comes too  warm, 
the  brass  ex- 
pands more  than 
the  iron,  and 
turns  the  rod  to 
the  right;  so  that 
it  makes  a  circuit 
which  cuts  off 
the  heat. 


NEED  OF   VENTILATION  217 

6.  In  what  way  are  gasoline  cans  commonly  distinguished  from 
cans  for  kerosene?    Why? 

7.  What  is  the  cause  of  the  " pounding"  often. heard  when  steam  is 
first  turned  on  in  a  cold  radiator? 

246.  Need  of  Ventilation. —  The  changes  that  take 
place  in  air  during  breathing  have  been  given  in  §  52. 
Ventilation  means  the  supplying  of  fresh  air  and  the 
removing  of  foul  air.  Our  houses  give  us  shelter,  warmth, 
and  a  host  of  comforts;  but  they  usually  rob  us  of  air. 
When  the  open  fireplace  was  used,  ventilation  required 
little  thought;  for  the  large  volume  of  air  that  passed  out 
through  the  chimney  was  constantly  replaced  by  fresh 
air  drawn  in  through  cracks  around  doors  and  windows, 
and  even  through  chinks  in  the  walls.  But  as  men  have 
built  tight-walled  houses,  used  weather  strips  and  storm 
windows  in  winter,  and  replaced  the  fireplace  by  stoves, 
furnaces,  and  steam  and  hot  water  heaters,  this  natural 
ventilation  has  largely  disappeared.  It  is  a  common 
experience  of  doctors  that  many  people  who  are  healthy 
enough  in  warm  weather,  when  doors  and  windows  are 
open,  have ' '  colds  "  and  throat  diseases  when  cold  weather 
comes  on.  One  reason  for  this  is  that  they  seal  up  most 
of  the  openings  through  which  fresh  air  can  enter  and 
foul  air  be  removed.  We  must  have  good  air  in  our 
houses,  or  we,  as  a  race,  are  doomed. 

The  way  in  which  tuberculosis,  or  consumption,  is  now  treated 
shows  the  importance  of  fresh  air.  Instead  of  being  protected  from  the 
outer  air  the  patient  is  now  told  to  live  in  a  tent,  in  the  open  air, 
winter  and  summer,  day  and  night.  Pure  air,  with  nourishing  food, 
has  been  found  to  be  an  almost  certain  cure  for  the  disease  in  its  early 
stages.  If  the  patient  will  do  his  part,  it  seems  as  though  nothing  can 


218        WATER,  HEAT,  AIR,  AND  LIGHT  IN  THE  HOUSE 

prevent  our  getting  control  of  the  "  Great  White  Plague,"  as  consump- 
tion is  called,  in  civilized  communities.  Many  healthy  persons, 
realizing  that  their  daily  work  gives  them  too  little  time  in  the  open 
air,  sleep  out-of-doors,  even  in  winter.  They  do  this,  not  only  without 
injury,  but  with  great  gain  in  health  and  vigor. 

247.  Methods  of  Ventilation. —  It  has  been  calculated 
that  during  one  hour  a  healthy  man  will  make  about 
4,000  cubic  feet  of  air  unfit  for  breathing.  This  is  the 
volume  of  a  room  20  x  20  x  10  feet.  Of  course  rooms  are 
not  air-tight;  hence  all  this  air  need  not  be  forced  into  a 
room  artificially.  The  Massachusetts  law  provides  that 
at  least  1,800  cubic  feet  of  fresh  air  shall  be  furnished  each 
pupil  each  hour  he  is  in  school.  If  the  amount  of  air 
furnished  to  a  schoolroom  is  below  this,  somebody  ought 
to  take  steps  to  get  better  ventilation. 

Recent  experiments  show  that  the  air  of  houses  becomes 
unfit  to  breathe,  not  so  much  because  it  contains  im- 
purities, as  because  it  is  stagnant.  Slightly  impure  air, 
if  in  motion,  is  better  than  highly  pure  air  that  is  not 
moving.  In  other  words,  the  greatest  need  is  circulation 
of  air. 

Where  steam  or  electric  power  can  be  obtained,  as  in  city  build- 
ings, and  in  factories,  heating  and  ventilation  are  often  carried  out 
together.  One  method  of  such  forced  ventilation  is  to  drive  warm, 
fresh  air  into  the  building  by  means  of  rotary  fans,  while  the  im- 
pure air  escapes  through  openings  made  in  the  walls  and  ceilings. 
Another  method  is  to  remove  the  impure  air  by  fans,  and  to  admit 
fresh,  warm  air  through  many  small  openings  near  the  floor.  Drafts 
are  thus  prevented.  The  air  is  usually  warmed  by  steam  coils  in  the 
basement. 

The  means  of  ventilation  may  also  be  used  to  cool  buildings  in  sum- 
mer, if  the  fresh  air  is  first  passed  over  ice. 


VENTILATION  WITHOUT  FANS 


219 


248.  Ventilation  without  Fans. —  If  there  is  no  system 
of  ventilation  in  the  house,  each  person  owes  it  to  himself 
to  provide  fresh  air  for  his  breathing.  Natural  ventilation 
depends  upon  the  simple  fact  that  heating  air  makes  it 
lighter,  so  that  it  rises,  while  cooling  it  makes  it  heavier, 
so  that  it  falls  (cf.  §  67).  We  must  remember  also  that 
in  winter  the  air  of  the  house  is  warmer  than  the  air  out- 
side; hence  fresh  air  naturally  enters 
through  the  cracks  at  the  bottoms  of 
doors  and  windows,  while  the  warm  air 
of  the  house  leaves  at  their  tops. 

Bedrooms.  The  windows  of  bedrooms 
should  be  left  open,  unless  storms  make 
this  actually  impossible.  An  excellent 
plan,  in  stormy  weather,  is  to  lower  the 
upper  sash  a  few  inches.  The  outside 
air  then  enters  between  the  sashes, 
while  the  air  of  the  room  leaves  at  the 
top  of  the  window.  If  a  board  having 
partly  boxed  holes  (Fig.  205)  is  placed  under  the  lower 
sash,  the  same  result  is  reached. 

Bedrooms  should  be  aired  thoroughly  during  the  day. 
The  fact  that  a  bedroom  is  kept  cold  does  not  mean  that 
its  air  is  pure;  cold  air  may  be  just  as  foul  as  warm  air,  if 
it  is  not  renewed  often  enough. 

Gas  stoves  or  kerosene  stoves  not  connected  with  a 
chimney  are  dangerous  in  closed  rooms,  since  they  produce 
carbon  dioxide  and  use  up  oxygen  (cf.  §  127). 

Schoolrooms.  Schoolrooms  that  are  not  ventilated  artificially 
should  have  each  of  several  windows  open  a  little,  rather  than  one  open 
wide.  In  this  way  strong  air  currents  (" drafts")  are  avoided.  If  the 


Fig.  205. 

How  to  Ventilate  a  Bed- 
room in  Stormy 
Weather. 


220        WATER,  HEAT,  AIR,  AND  LIGHT  IN  THE  HOUSE 

wind  is  blowing  strongly,  the  openings  should  be  on  the  side  opposite 
the  wind. 

When  a  large  room  is  heated  by  a*stove,  the  stove  should  be  sur- 
rounded by  a  "drum,"  open  at  the  top  and  bottom,  and  reaching  from 
near  the  floor  to  a  point  some  distance  above  the  stove-top.  The 
drum  should  be  in  two  parts,  hinged  together,  so  that  the  stove  may  be 
easily  reached.  The  circulation  of  air  in  the  room  is  then  not  left  to 
chance;  for  the  drum  not  only  protects  those  nearest  the  stove  from 
excessive  heat,  but  it  also  sets  up  useful  convection  currents.  These 
bring  cold  air  from  the  farthest  parts  of  the  room  to  the  stove,  heat  it, 
and  then  carry  it  away  along  the  ceiling.  The  room  is  thus  heated 
evenly,  and  ventilated  at  the  same  time. 

Healing  Systems  and  Ventilation.  The  hot-air  furnace  brings  in 
fresh,  warm  air;  but  the  removal  of  the  cooled,  foul  air  is  left  to  the 
cracks  of  the  room.  The  fireplace,  since  its  opening  is  near  the  floor, 
is  an  excellent  aid  to  the  hot-air  furnace.  Stoves  provide  some  ven- 
tilation; since  fresh  air  from  outside  must  come  in  to  take  the  place  of 
the  air  that  goes  through  the  stove.  Hot  water  and  steam  heating 
systems  of  themselves  give  no  ventilation. 

249.  Need  of  Moisture  in  Air. —  One  very  important 
constituent  of  fresh  air  must  not  be  forgotten :  its  mois- 
ture. We  find  air  very  comfortable,  at  any  given  tempera- 
ture, if  it  has  between  2/5  and  2/s  of  the  water  it  can  hold 
at  that  temperature.  Such  air  takes  up  the  perspiration 
at  a  moderate  rate,  and  so  regulates  the  heat  of  the  body. 
But  if  the  moisture  is  more  than  2/s  of  what  the  air  can 
hold,  we  are  uncomfortable;  the  perspiration  does  not 
evaporate  rapidly  enough,  and  the  air  feels  "sticky." 
When  too  little  moisture  is  present,  the  perspiration  evapo- 
rates too  rapidly.  The  skin  then  becomes  parched  and  dry. 

As  a  result  of  artificial  heating  and  ventilation  the 
amount  of  air  moisture  in  a  house  is  almost  sure  to  be  too 
small.  The  reason  for  this  is  that  the  cold  air  entering  a 


GLASS  221 

house  has  its  power  of  holding  water  increased  by  warm- 
ing. The  actual  amount  of  water  is  not  changed;  but  the 
amount  that  the  air  holds  as  compared  with  what  it  is 
able  to  hold  is  decidedly  smaller.  Hence  it  takes  too 
much  moisture  from  our  bodies.  A  well-known  authority 
says  that  the  moisture  in  the  air  of  a  room  should  be  such 
that  dew  and  frost  are  deposited  on  the  inside  of  windows 
in  cold  weather.  If  steam  or  hot  water  are  used  for  heat- 
ing, a  shallow  dish  of  water  should  be  kept  in  the  room. 
In  the  hot-air  furnace  a  water  pan  is  provided  inside  the 
air  box.  This  should  be  kept  full. 

250.  Light  in  the  House. —  The  problem  of  lighting 
the  house  properly  is   a  very  serious   one.     Primitive 
peoples,  and  even  our  own  ancestors  of  a  few  generations 
ago,  could  afford  but  little  sunlight  in  their  houses,  free 
as  it  is  out  of  doors.     This  was  because  they  had  no  cheap 
transparent  substance  like  our  modern  glass.     They  had 
only  oiled  paper,  or  thin  sheets  of  horn,  isin-glass  (the 
mineral  mica;  cf.  §  285),  etc.     But  the  common  people 
could  not  afford,  or  get,  much -of  these  materials;  so  their 
houses  were  dark.     The  problem  of  sunlight  is  so  impor- 
tant to  the  general  health,  as  well  as  to  sight,  that  the  men 
who  made  cheap  glass  possible  must  be  ranked  among 
the  greatest  benefactors  of  the  race.     Darkness  in  the 
house  means  dirt  and  filth,  and  where  these  exist  disease 
and  pestilence  are  sure  to  get  a  foothold. 

251.  Glass. —  Glass  is  made  out  of  a  mixture  of  sand, 
limestone,  and  soda  (or  sodium  sulphate  instead  of  soda). 
The  mixture  is  melted  in  fire-clay  pots  about  4  feet  high 


222        WATER,  HEAT,  AIR,  AND  LIGHT  IN  THE  HOUSE 


and  4  feet  in  diameter,  and 
forms  a  clear,  transparent 
liquid.  When  this  is  cooled, 
it  forms,  before  it  hardens,  a 
pasty  mass.  While  the  glass 
is  pasty,  vessels  and  other 
objects  can  be  made  from  it, 
and  it  can  be  "blown"  into 
many  shapes. 

Window  glass  is  made  by  work- 
men who  blow  the  pasty  glass  (Fig. 
206)  into  the  form  of  a  cylinder, 

and  then  cut  the  cylinder  open  lengthwise,  so  that  it  forms  a  sheet. 

In  a  new  process,  glass  is  also  drawn  out  by  a  machine  into  sheets 


Fig.  206. 
Blowing  Window  Glass. 


Fig.  207. 

Casting  Plate  Glass  at  the  Saint  Gobain  Manufactory,  France. 
Scientific  American  Supplement. 


From  the 


ARTIFICIAL  LIGHTING 


223 


of  any  desired  width  and  of  varying  thickness  (Scientific  American 
Supplement,  No.  1689). 

Plate  glass  is  made  by  the  pouring  of  melted  glass  upon  hot  iron 
plates;  heated  rollers  flatten  it  out  (Fig.  207). 

252.  Artificial  Lighting.— Until  about  1860  the  only 
common  means  of  lighting  were  the  fireplace,  candles,  and 
oils.  Among  the  oils  used  were  lard,  olive,  and  whale 
(sperm)  oils.  The  oils  burn  with  a  smoky  flame;  but  by 
the  use  of  a  wick  they  are  drawn  up  (cf.  §  32),  a  little  at  a 
time,  and  converted  into  vapor.  It  is  this  vapor  that 
burns.  The  oils  have  a  very  high  boiling  point;  hence 
there  is  little  danger  that  the  body  of  the  oil  will  be  set 
on  fire  (cf.  §  122). 

Candles.  The  materials  used  for  candles  are  waxes, 
fats,  and  paraffin.  Waxes  are  high-melting  fats,  just 
as  oils  are  low-melting  fats  (cf.  §  224).  The  making  of 


Fig.  208. 

Modern  Way  of  Making  Candles,     In  some  of  the  candle-moulding  machines  more  than 

500  candles  can  be  made  at  once.     Courtesy  of  Roman  and  Company, 

Cincinnati,  Ohio. 


224        WATER,  HEAT,  AIR,  AND  LIGHT  IN  THE  HOUSE 


candles  originally  took  place  in  the  household,  and  in- 
volved much  painstaking  work.  A  wick  was  dipped  into 
the  melted  fat,  allowed  to  cool,  and  then  dipped  again, 
until  the  desired  thickness  was  obtained. 

In  modern  candle-making  (Fig.  208)  the  wick  is  set  in  a 
mould,  and  the  melted  fatty  material  or  paraffin  (cf. 
§  121)  is  poured  around  it  in  the  mould.  In  former  times 
"snuffers"  were  required  to  remove  the  charred  wick 
inside  the  flame;  nowadays,  snuffers  are  not  needed. 
The  reason  for  this  is  that  in  the  modern  candle  one  of  the 
threads  of  the  wick  is  pulled  more  tightly 
than  the  others.  As  a  result  the  tip  of 
the  wick  curves  outward  to  the  edge  of 
the  flame  (Fig.  42,  §  49),  where  the  air 
oxidizes  it  completely. 

Kerosene  Lamps.  The  discovery  of  petroleum 
in  Pennsylvania  in  1859  (cf.  Fig.  98,  §  121)  had 
a  decided  effect  upon  the  world's  lighting  and 
heating  problems;  for  it  furnished  gasoline,  kero- 
sene, paraffin,  etc.  Gasoline  has  too  low  a  flash- 
ing point  (cf.  §  122)  to  permit  its  use  with  a  wick, 
in  lamps.  Kerosene  cannot  be  burned  with  a 
wick  alone,  as  the  true  oils  can  (cf.  §  224) ,  because 
it  smokes.  To  increase  the  air  supply,  and  so  to 
prevent  smoking,  kerosene  lamps  have  chimneys. 
The  heated  air  and  gases  carried  upward  by  convection  create  a  draft; 
thus  fresh  portions  of  air  are  drawn  into  the  burner  below  the  flame. 

To  increase  the  amount  of  kerosene  that  can  burn  in  a  given  time, 
and,  therefore,  to  get  a  more  intense  light,  men  use  central  draft 
burners.  These  have  circular  wicks  (Fig.  209),  and  air  is  drawn  to  the 
inside  of  the  circular  flame  as  well  as  to  the  outside  of  it. 

253.  Gas  for  Lighting. —  Illuminating  gas  is  formed 
when  soft  coal  is  heated  in  closed  retorts  (cf.  §  124),  and 


Fig.  209. 

Central  Draft  Burner. 
Air  gets  at  the  wick 
both  inside  and  out- 
side. 


GAS  PIPES  AND  FIXTURES  225 

when  steam  is  passed  through  a  bed  of  hot  hard  coal  or 
coke.  The  second  method  gives  water  gas.  At  present 
nearly  all  illuminating  gas  is  water  gas  il enriched"  with 
gases  obtained  by  the  charring  of  petroleum;  these  make  it 
light-producing. 

As  illuminating  gas  comes  to  the  consumer,  it  burns 
with  a  brilliant,  yellow  flame.  If  burned  from  a  circular 
opening,  it  is  smoky;  but  if  we  force  it  through 
a  narrow  slit  (a  "tip"),  it  is  almost  smokeless, 
because  the  gas  has  a  large  surface  in  contact 
with  the  air. 

254.  Incandescent  Mantles. — To  get  a  brighter  light 
than  that  of  the  ordinary  gas  flame,  we  may  burn  the 
gas  in  a  Bunsen  burner,  and  put  a  "mantle"  in  its  hot, 
colorless  flame.    This  is  the  principle  of  the  Welsbach       Fig-  21°; 
and  other  " mantle"  lamps.     The  light  comes  from  the    A  gas  stream 
incandescent  (white  hot)  mantle  (Fig.  210). 

The  best  mantles  contain  the  oxides  of  the  two  rare 
metals  cerium  and  thorium.     The  mantle  is  first  knitted    °xi<jesto  white 

neat. 

out  of  "stockingette."  This  is  then  soaked  in  a  solution 
containing  cerium  and  thorium  salts.  When  the  stockingette  is  dried, 
the  solid  salts  fill  its  pores.  The  mantle  is  now  set  on  fire.  The 
organic  part  (the  thread)  burns  up,  and  the  salts  in  its  pores  are 
decomposed.  The  oxides  of  the  metals  remain  as  a  thin,  fragile  shell. 
Other  gases,  such  as  natural  gas  and  gasoline  vapor,  can  be  used  with 
incandescent  mantles. 

255.  Gas  Pipes  and  Fixtures. —  Gas  is  stored  by  the 
gas  company  in  large  tanks  inverted  in  water.     They  are 
loaded  with  weights,  which,  with  the  weight  of  the  tanks, 
cause  the  pressure  of  the  gas.     As  gas  is  used  up,  the 
tanks  sink  into  the  water;  but  they  rise  again  when  they 
are  refilled. 


226        WATER,  HEAT,  AIR,  AND  LIGHT  IN  THE  HOUSE 


Gas 


The  pipes  that  carry  the  gas  underground  to  the  con- 
sumer are  of  iron;  sometimes  they  are  3  or  4  feet  in  diam- 
eter. The  pipes  from  the  street  "main"  into  the  house 
and  to  the  gas  outlets  are  also  of  iron.  The  smaller  pipes 
are  joined  by  screw  joints,  made  gas-tight  by  some  pasty 
mixture,  such  as  red  lead  and  glycerine.  The  gas  com- 
pany tests  the  whole  piping  system  of  a  house  by  pump- 
ing air  into  it  until  there  is  considerable  pressure.  The 
pressure  is  measured  by  a  gauge,  or  manom- 
eter (Fig.  211).  The  gas-fitter  needs  to  be 
careful,  or  he  will  break  some  of  the  joints 
when  he  attaches  the  fixtures. 

The  "key,"  by  which  gas  is  turned  on  or  off  in  a 
fixture,  is  a  tapering  plug  having  an  external,  flat 
handle.  The  plug  fits  into  a  hole  with  tapering  sides. 
To  hold  the  plug  tight  in  its  socket,  there  is  a  short, 
spiral  spring.  This  is  held  in  place  by  a  screw  that 
presses  against  the  body  of  the  fixture.  If  the  key  or 
its  socket  wears  away,  so  that  gas  escapes  around  it, 
the  joint  may  be  tightened  by  a  slight  turning  of  the 
screw.  We  must  remember  that  illuminating  and 
fuel  gases  usually  contain  much  carbon  monoxide,  a  very  poisonous 
gas,  and  that  all  leaks  in  the  gas  fixtures  should  be  attended  to  im- 
mediately. 

256.  The  Gas  Meter. —  In  most  houses  the  gas  meter 
is  found  in  the  basement.  It  is  a  metal  box  having,  on  its 
face,  dials  like  those  of  Fig.  212.  When  the  hand  on  the 
1 '  5  cubic  feet "  dial  has  revolved  20  times,  the  hand  on  the 
"1000  cubic  feet"  dial  will  have  moved  from  0  to  1,  and 
will  indicate  100  cubic  feet.  The  hand  on  the  "1,000" 
dial  must  make  one  complete  revolution  to  move  the  hand 
on  the  "10,000"  dial  from  0  to  1,  and  so  on.  Note  in 


Fig.  211. 
The  gas  pushes 
up  the  mercury 
until  the  down- 
ward pressure 
of  the  mercury 
equals  the  gas 
pressure. 


ACETYLENE  FOR  LIGHTING 


227 


what  direction  each  of  the  hands  of  Fig.  212  must  have 
moved  to  come  to  its  present  position;  then  write  down 
the  meter  "reading"  shown  in  the  figure. 

The  gas  meter  consists  of  two  compartments  the  size  of  which  is 
controlled  by  two  movable  diaphragms,  or  disks.  The  diaphragms  are 
forced  inward  and  outward  by  the 
pressure  of  the  gas  from  the  city 
"mains."  A  " slide  valve "  (cf.  §  24, 
Fig.  19)  changes  the  course  which 
the  gas  must  take,  so  that  the 
compartments  may  be  first  filled, 
and  then  emptied.  As  the  dia- 
phragms move  back  and  forth, 
they  give  their  motion  to  the  re- 
cording hand  of  the  dial.  Since 
the  capacity  of  the  compartments 
is  known,  and  the  dial  shows  how 
many  times  the  compartments  have  been  filled  and  emptied,  the  dial 
also  shows  how  many  cubic  feet  of  gas  have  passed  through  the 
meter. 


Fig.  212. 

Gas  Meter.    The  dials  read  up  to  5,  1,000, 

10,000,  and  100,000  cubic  feet, 

respectively. 


257.  Acetylene  for  Lighting.— Acetylene  (cf.  §§  120 
and  158)  is  made  by  the  action  of  water  upon  calcium 
carbide.  It  contains  a  large  proportion  of  carbon,  and 
burns  with  a  very  smoky  flame.  Hence  the  acetylene 
burner  must  be  different  from  an  ordinary 
gas  burner.  The  most  common  form  is 
shown  in  Fig.  213.  In  this  burner  the 
acetylene  is  mixed  thoroughly  with  air, 
and  the  two  jets  of  burning  gas  are  made 
to  strike  each  other.  The  result  is  an  out- 
spread, "fish-tail"  flame.  It  is  smokeless, 
and  of  brilliant  whiteness. 


Fig.  213. 


A  Burner  for  Acety- 
lene Gas. 


228        WATER,  HEAT,  AIR,  AND  LIGHT  IN  THE  HOUSE 


258.  Electric  Lighting. —  The  principle  of  the  arc  and 
incandescent  electric  lamps  has  already  been  given  (cf. 
§  157).     The  filaments  of  modern  incandescent  lamps  are 
made  of  the  rare  elements  tungsten  and  tantalum,  as  well 
as  of  carbon.     Tungsten  and  tantalum  lamps  cost  more 
than  carbon  lamps;  but  they  use  much  less  electric  energy 
to  produce  a  given  amount  of  light. 

It  is  very  important  to  have  a  house  properly  " wired"; 
for  if  wires  that  are  close  together  lose  their  insulation, 
we  have  the  accident  known  as ' '  crossed  wires,"  or ' '  short- 
circuiting."  If  the  wires  were  of  large  diameter,  this 
accident  would  not  be  particularly  serious.  But  as  copper 
is  expensive,  the  smallest  possible  wires  are  used,  and  these 
are  often  unable  to  carry  the  "load"  suddenly  put  upon 
them.  They  become  hot,  and  may  set  the  house  on  fire. 
To  avoid  the  rise  of  temperature  in  a 
circuit  to  the  danger  point,  the  electri- 
cian places  a  "fuse  box"  (Fig.  214) 
in  the  house.  To  "fuse"  means  to 
"melt." 

The  fuse  box  contains  a  number  of  wires 
made  out  of  a  low-melting  mixture  (alloy)  of 
metals.  One  of  these  is  placed  in  each  circuit. 
If  for  some  reason  the  amount  of  current  in  a 
circuit  becomes  too  great,  the  melting  of  the 
fuse  breaks  the  circuit,  and  prevents  a  fire. 

The  fuse  box  of  a  house  usually  contains, 
also,  the  switch  that  controls  all  the  electric  circuits  of  the  house. 
When  any  repairing  of  wires  or  outlets  is  to  be  done,  the  house  current 

should  be  cut  off  by  means  of  this  switch. 

".  .  • 

259.  The  Electric  Meter. —  The  work  done  by  the  elec- 
tric current  (cf.  §  25)  is  measured  in  watt-hours,  or  in 


USE   METAL 


Fig.  214. 
A  Fuse  Box. 


SUMMARY 


229 


kilowatt-hours.  The  kilowatt  is  1,000  watts  (cf.  §  9: 
kilogram,  kilometer,  etc.).  A  kilowatt  is  equal  to  1.34 
horse  powers  (cf.  §  26).  A  kilowatt-hour  is  an  electric 
power  of  one  kilowatt  working  for  one  hour.  It  is  the 
common  unit  used  by  electric  companies  in  selling  power 
to  consumers.  The  watt  is  named  for  James  Watt,  the 
inventor  of  the  steam  engine  (cf.  §  24). 

The  common  electric  watt-hour  meter  is  really  a  tiny,  finely-built 
electric  motor  (cf.  §  161).  The  "field"  of  the  electromagnets  of  the 
motor  is  produced  by  the  current  to  be  measured,  and  exerts  force 
on  the  "armature,"  causing  it  to  revolve.  The  armature  is  delicately 


KILOWATT  HOURS 


Fig.  215. 
Electric  Kilowatt-Hour  Meter. 

mounted,  on  steel  balls  and  jewels.  As  the  armature  revolves,  it  gives 
motion  to  clock  gear-wheels,  and  these  in  turn  move  the  hands  of 
the  dials  (Fig.  215).  Note  the  direction  in  which  the  hand  of  each  dial 
has  moved  to  bring  it  to  its  present  position,  and  write  down  the  read- 
ing of  the  meter. 

260.  Summary. —  Modern  conveniences  are  due  to  scientific  dis- 
coveries and  their  application. 

We  need  an  abundance  of  water  for  our  houses,  our  industries,  and 
our  community  life. 

Plumbing  is  the  system  of  pipes,  etc.,  that  brings  water  to  the 
house,  and  carries  water  and  waste  away  from  it. 

Traps  keep  sewer  air  out  of  the  house. 


230        WATER,  HEAT,  AIR,  AND  LIGHT  IN  THE  HOUSE 

Matches  raise  combustibles  to  their  kindling  temperatures. 

The  fireplace  is  not  only  an  ornament,  but  a  means  of  ventilation. 

Cooking  stoves  have  roundabout  flues  through  which  the  hot 
gases  must  travel;  these  heat  the  ovens. 

Gas  stoves  are  Bunsen  burners. 

Gasoline  must  be  treated  like  an  inflammable  gas. 

Electric  heaters  are  circuits  with  high  resistance;  they  turn  the 
current  into  heat. 

Hot-water  heating  depends  on  convection  currents  in  heated  water; 
steam  heating  depends  on  the  heat  given  'off  in  .the  condensation  of 
steam. 

The  thermostat  depends  upon  the  unequal  expansion  and  con- 
traction of  different  metals. 

Ventilation  is  necessary  for  successful  indoor  living.  It  may  be 
natural  or  forced,  but  should  not  be  left  to  chance. 

Proper  amount  of  moisture  is  as  necessary  as  proper  amount  of  air. 

Cheap  glass  is  a  great  civilizing  agent. 

For  lighting,  man  uses  candles,  oils,  petroleum  products,  gas, 
acetylene,  electricity,  etc. 

Incandescent  mantles  consist  of  oxides  of  certain  metals. 

The  gas  meter  records  the  amount  of  gas  that  passes  from  the 
" mains"  to  the  house. 

Electric  circuits  become  hot  from  "short-circuiting."  Fire  is 
prevented  in  such  circuits  by  means  of  "fuse  wires." 

Electric  power  is  sold  by  the  kilowatt-hour. 

Electric  meters  are  small,  finely-built  motors. 

261  Exercises. 

1.  What  means  of  ventilation  are  there  in  your  house?    Are  they 
used? 

2.  If  you  open  the  door  of  a  warm  room,  and  hold  a  burning  match 
at  the  top  of  the  opening,  in  what  direction  will  the  flame  be  drawn? 
In  what  direction  will  it  be  drawn  at  the  bottom  of  the  doorway? 
Explain.       * 

3.  Show  that  the  hot-air  furnace  is  simply  an  improved  form  of  a 
heating  stove  surrounded  by  a  "drum." 


EXERCISES  231 

4.  For  what  reasons  is  the  size  of  the  windows  of  our  houses  an 
important  matter  from  the  point  of  view  of  public  health? 

5.  What  are  the  uses  of  plate  glass?    Find  out  what  materials  are 
used  in  making  optical  glass;  that  is,  glass  for  spectacles,  lenses,  etc. 

6.  How  does  it  happen  that  so  many  candles  are  used  nowadays, 
when  there  are  so  many  other  ways  of  producing  light? 

7.  If  you  "blow  out"  a  candle  or  kerosene  flame,  you  can  relight  it 
by  holding  a  lighted  match  some  distance  above  the  wick.     Explain. 

8.  When  a  carbon  incandescent  lamp  is  old,  its  globe  becomes  very 
hot  while  in  use.     Are  you  economical  if  you  continue  using  it  longer? 
Explain  why. 

9.  What  kind  of  gas  does  your  family  use  for  lighting  and  heating? 
How  much  does  it  cost  per  thousand  cubic  feet?     How  much  did  you 
use  last  month? 

10.  What  kind  of  incandescent  lamps  do  you  use  at  home?    How 
much  does  each  cost?    How  long  is  the  "life"  of  each  lamp?    For 
what  reasons  is  one  of  your  electric  lamps  discarded? 

11.  What  is  the  price  of  electricity  per  kilowatt-hour  in  your  city? 
How  much  did  your  family  use  last  month? 


CHAPTER  XIII 

THE  WEATHER 

262.  Causes  of  Weather. —  We  have  already  learned 
much  about  the  earth's  atmosphere:  its  composition, 
density,  and  pressure  (cf.  §§  38  ff.);  also  about  gases: 
that  they  expand  when  heated,  or  when  exposed  to  a 
lower  pressure;  that  they  contract  when  cooled,  or  when 
put  under  a  higher  pressure;  that  they  give  off  heat  when 
compressed,  but  absorb  it  when  expanded.  We  have  also 
studied  about  water:  its  three  physical  states,  its  great 
heat  capacity,  and  its  presence  in  the  atmosphere.  These 
topics  form  the  basis  of  our  study  of  the  weather,  and 
should  be  reviewed  carefully.  By  "weather"  we  mean 
the  changing  conditions  of  the  earth's  atmosphere,  such 
as  its  temperature,  its  pressure,  and  the  amount  of 
moisture  it  contains;  the  cloudiness  or  fairness  of  the  sky; 
the  amount  of  rainfall  or  snowfall;  the  velocity  of  the 
wind,  and  its  direction. 

As  we  look  over  this  list  of  "  conditions  of  the  weather, " 
we  find  that  they  are  really  the  properties  of  two  sub- 
stances :  air,  as  we  find  it  in  that  great  ocean,  the  atmos- 
phere; and  water,  which  enters  the  atmosphere  so  readily 
by  evaporation  from  seas,  lakes,  and  rivers,  and  which 
leaves  the  atmosphere  again  as  clouds,  rain,  dew,  snow, 
and  frost. 

The  average  of  all  the  weather  conditions  for  any  given 
place  is  the  climate  of  that  place. 

232 


CHANGES  IN   THE  DENSITY  OF  AIR  233 

263.  Changes  in  the  Density  of  Air. —  If  we  can  imagine 
that  there  is,  near  the  earth's  surface,  a  layer  of  air  all  of 
about  the  same  density,  and  if  we  also  imagine  that  some 
of  this  air  becomes  heated,  we  can  understand  how  as- 
cending air  currents  are  produced  (cf.  §  67).  We  say  that 
the  heated  air  "rises";  what  really  happens  is  that  the 
surrounding,  heavier  air  is  pulled,  by  gravity,  into  the 
place  occupied  by  the  heated,  lighter  air,  and  the  heated 
air  is  pushed  up  in  the  form  of  a  current.  The  movement 
of  the  air  in  currents  must,  of  course,  be  more  rapid  than 
the  diffusion  of  gases  (cf.  §  106),  or  the  lighter  air  will  be 
mixed  with  the  heavier  air,  and  there  will  be  no  convection. 

Air  is  made  lighter,  not  only  when  it  is  heated,  but  also 
when  it  takes  up  moisture.  Steam  has  a  lower  density 
than  air  (cf.  Appendix,  Table  IV) ;  hence  air  that  is  mixed 
with  much  of  it  will  be  decidedly  lighter  than  dry  air  at 
the  same  temperature. 

How  high  will  an  ascending  air  column  go?  It  will  rise 
until  it  reaches  a  level  at  which  its  density  is  the  same  as 
that  of  the  air  surrounding  it.  Then  it  will  be  flattened 
out  as  horizontal  currents  (winds);  in  time  these  will 
descend  again  to  the  earth.  In  this  way  we  get  ' '  circu- 
lation" in  the  atmosphere. 

Since  the  pressure  of  the  atmosphere  depends  on  the  density  of  the 
air,  a  barometer  (cf.  §  40)  placed  in  a  region  from  which  air  is  ascending 
will  show  that  the  region  is  an  "area  of  low  pressure."  The  weather 
observer  reads  the  atmospheric  pressure  from  his  barometer,  and  uses 
this  pressure  in ' '  forecasting  "  the  weather ;  but  we  must  remember  that 
the  barometer  tells  only  the  pressure  of  the  atmosphere.  If  we  wish 
to  draw  any  conclusions  regarding  the  weather,  we  need  other  facts  in 
addition  to  the  barometer  reading. 

The  aneroid  barometer  is  more  convenient  to  carry  about  than  the 


234  THE  WEATHER 

mercury  barometer.  It  consists  of  a  metal  box  from  which  the  air 
has  been  removed.  One  side  of  the  box  is  connected  by  a  system  of 
levers  with  a  pointer  that  shows  the  atmospheric  pressure.  When  the 
pressure  increases,  the  side  of  the  box  is  pushed  inward,  and  the  pointer 
moves  forward.  When  the  pressure  becomes  lower,  the  side  of  the  box 
springs  back  into  place,  and  the  pointer  moves  backward. 

264.  Heating  of  the  Air. —  The  final  source  of  the  heat 
of  the  earth's  surface  is  the  sun  (cf.  §  76).  The  sun's 
rays  give  up  part  of  their  heat  to  the  atmosphere  as  they 
pass  through  it.  But  a  much  larger  part  of  the  sun's 
heat  reaches  the  earth's  surface.  This  portion  is  partly 
reflected  back  into  the  atmosphere  and  into  space,  and 
partly  absorbed  (cf.  §§  173  and  176)  by  the  earth.  The 
part  absorbed  warms  the  land  and  the  water  for  a  time; 
afterwards  it  is  given  back  to  the  air.  The  total  amount 
of  heat  absorbed  by  the  atmosphere  has  been  estimated  to 
be  about  70  per  cent  of  the  amount  received  from  the 
sun.  Of  course  this  absorption  is  only  temporary;  for  in 
the  end  the  quantity  received  and  the  quantity  lost  are 
practically  the  same. 

The  lower  part  of  the  atmosphere  absorbs  heat  much 
better  than  the  upper  part,  and  becomes  warmer.  The 
reasons  for  this  are  that  the  lower  air  is  denser,  and  that 
it  has  more  impurities :  dust,  smoke,  clouds,  carbon  diox- 
ide, and  water  vapor.  All  of  these  enable  the  atmosphere 
to  hold  its  heat.  It  is  these  good  absorbers  that  make 
the  atmosphere  a  trap  for  the  sun's  energy,  and  a  blanket 
to  prevent  too  rapid  heating  and  cooling  (cf.  §  183). 

Air  is  also  heated  and  cooled  by  its  own  contraction  and  expansion, 
respectively  (cf.  §  71).  As  it  ascends,  and  therefore  expands,  it 
becomes  colder.  This  is  the  reason  why  ascending  air  currents  finally 


MOISTURE  OF   THE  AIR  235 

reach  levels  beyond  which  they  cannot  go;  they  must  spread  out  as 
horizontal  winds  (cf.  §  263).  When  the  cold,  upper  air  falls  to  levels 
having  a  greater  density,  the  opposite  effect  is  observed:  the  air  is 
compressed,  and  becomes  warmer.  Thus  cold  air  that  comes  tumbling 
down  the  slopes  of  the  Alps  into  the  Swiss  valleys  is  often  changed  into 
a  hot  wind  (the/oe/m),  because  of  its  own  compression. 

265.  Moisture  of  the  Air. —  As  we  have  already  learned 
(cf.  §  89),  water  changes  into  steam  (evaporates)  at  all 
ordinary  temperatures.  In  the  open  air  the  amount  of 
evaporation  usually  seems  to  have  no  limit;  this  is  true 
because  drafts  arid  winds  constantly  carry  new  portions 
of  air  over  the  water,  and  remove  the 
air  that  has  already  taken  up  water. 
But  when  we  have  an  enclosed  volume 
of  air  over  water,  only  a  limited 
evaporation  of  the  water  can  take  • 

place;  this  is  the  same  as  saying  that,       g 

at  a  given  temperature,  only  a  limited  Kg.  216. 

,        £  i    •      ,  Bell  Jar  of  Air  over  Water. 

amount  01  steam  can  expand  into  a 
given  space  or  can  mix  itself  with  (diffuse  into)  a  given 
volume  of  air.  Figure  216  shows  such  an  enclosed 
volume  of  air.  At  first  water  evaporates  rapidly  into  the 
air  of  the  jar;  but  after  a  time  the.  amount  of  moisture 
(steam)  becomes  no  greater,  no  matter  how  long  the 
apparatus  is  allowed  to  stand.  The  water  does  not  cease 
evaporating,  but  the  steam  is  condensed  to  water  as  rapid- 
ly as  the  water  is  changed  to  steam.  The  condition  of  the 
air,  or  the  space,  in  the  jar  is  then  like  that  of  a  sponge 
filled  with  water;  we  say  that  the  air  is  saturated  with 
water  vapor.  If  we  raise  the  temperature,  the  air  be- 
comes unsaturated,  although  it  was  saturated  at  the  lower 


236  THE  WEATHER 

temperature.  More  water  will,  therefore,  change  to 
steam  and  mix  itself  with  the  air  of  the  jar.  But  if  we 
lower  the  temperature  of  air  that  is  saturated,  enough  of 
the  steam  will  be  condensed  to  leave  the  air  just  saturated 
at  the  lower  temperature. 

266.  Humidity. —  The  weight  of  the  water  that  is  present  in  a  given 
volume  of  air  is  called  the  humidity  of  the  air.     The  humidity  is  stated 
as  so  many  grains  of  water  for  each  cubic  foot  of  air,  or  as  so  many 
milligrams  of  water  for  each  liter  of  air.    A  cubic  foot  of  air  or  space 
at  50°  F.  can  hold  4  grains  of  water  vapor;  if  saturated  at  80°  F.,  it 
can  hold  11  grains.     The  cubic  foot  saturated  at  50°  F.  with  4  grains 
of  water  is  unsaturated  at  80°  F.     It  has,  in  fact,  only  yn,  or  36  per 
cent,  of  the  amount  needed  to  saturate  it  at  80°  F. 

The  amount  of  water  actually  present  in  a  volume  of  air  or  space, 
divided  by  the  amount  the  air  or  space  would  hold  if  it  were  saturated, 
is  called  the  relative  humidity  of  the  air  or  space.  In  the  case  given,  the 
relative  humidity  is  36  per  cent  (cf.  §§  249  and  267). 

267.  Dew  and  Frost. —  Dew  and  frost  are  moisture 
deposited  directly  from  the  air,  upon  cool  objects.     We 
see  dew  formed  when  a  pitcher  of  cold  water  "sweats" 
on  a  hot  day.     In  Nature,  dew  is  commonly  formed  after 
sunset,  when  the  air  and  bodies  near  the  ground  radiate 
their  heat,  and  grow  cool.     Stones,  grass  blades,  etc.,  cool 
more  rapidly  than  the  air,  and  their  temperature  falls 
below  that  at  which  the  air  is  saturated.     They  therefore 
cool  the  air  near  them,  so  that  it  deposits  some  of  its 
moisture  upon  them.     The  temperature  to  which   air 
must  be  cooled  so  that  it  will  just  deposit  moisture  is 
called  the  dew  point.     If  the  dew  point  is  below  0°  C.,  frost 
is  formed  instead  of  dew. 

A  clear  night  favors  the  forming  of  dew  and  frost, 


FOGS  AND   CLOUDS  237 

because  the  earth  and  the  air  cool  more  rapidly  if  clouds 
are  not  present  (cf.  §  264).  A  gentle  breeze  favors  dew 
formation,  because  it  brings  fresh  supplies  of  almost 
saturated  air  to  the  cooling  objects.  A  strong  wind  is 
not  favorable,  for  it  does  not  allow  the  air  to  remain  long 
enough  in  contact  with  the  cool  objects. 

Fruit  growers  know  that  there  must  be  air  drainage 
as  well  as  water  drainage  in  their  orchards.  If  an  orchard 
is  placed  in  a  hollow,  cold  air  will  fall  into  it  as  water 
would,  and  may  cause  damaging  frosts, 
while  neighboring  orchards  situated  on 
the  tops  or  slopes  of  hills  may  escape 
injury. 

The  dew  point  may  be  found  at  any  time  by  the 
use  of  the  apparatus  of  Fig.  217.  A  polished  metal 
beaker  containing  water  is  stirred  with  a  ther- 
mometer, and  bits  of  ice  are  added  from  time  to 
time.  The  temperature  reached  when  dew  is  Fig.  217. 

just  formed  on  the  outside  of  the  beaker  is  the 
dew  point. 

We  can  use  the  dew  point  to  determine  the  relative  humidity  of  the 
air  (cf.  §  266).  Such  determinations  are  valuable  in  greenhouses,  in 
schoolrooms,  and  in  your  own  house  (cf.  §  249).  Let  us  suppose  that 
the  temperature  of  a  room  is  23°  C.  In  the  Appendix,  Table  VIII, 
we  find  that  the  pressure  of  water  vapor  (cf.  §  89)  at  23°  C.  is  20.9  mm. 
This  would  be  the  pressure  of  the  water  vapor  in  the  air  at  23°  C.,  if 
the  air  were  saturated  with  it.  Suppose  that  we  find  the  dew  point 
to  be  10°  C.  Table  VIII  shows  that  at  this  temperature  the  pressure 
of  water  vapor  is  9.1  mm.  The  air  of  the  room  has,  therefore,  less 
than  half  its  capacity  of  water  (9.1  divided  by  20.9  is  0.44,  or  44  per 
cent,  the  relative  humidity). 

268.  Fogs  and  Clouds. —  If  the  air  just  above  the 
ground  is  cooled  below  the  dew  point,  its  water  is  con- 


238  THE  WEATHER 

densed  in  tiny  droplets,  and  we  have  a  fog.  If  a  fog  is 
formed  some  distance  above  the  earth,  we  call  it  a  cloud. 
Some  clouds  consist  of  ice  particles. 

Clouds  and  fogs  are  not  permanent,  but  may  be  ab- 
sorbed again  if  the  temperature  of  the  air  is  raised  above 
the  dew  point,  as  it  often  is  by  the  rising  sun.  But  even 
while  a  cloud  lasts  it  is  both  losing  water  particles  and 
gaining  them.  Many  persons  think  that  clouds  are  lighter 
than  air,  and  float  in  the  air.  This  is  not  so;  cloud  par- 
ticles are  heavier  than  air,  and  settle  slowly  toward  the 
earth.  But  as  they  reach  a  layer  of  unsaturated  air, 
they  evaporate  and  disappear.  This  level,  at  which  com- 
plete evaporation  takes  place,  is  the  bottom  of  the  cloud. 
Clouds  also  extend  outward  until  their  water  particles 
evaporate  as  rapidly  as  they  are  supplied.  It  is  because 
cloud  material  is  constantly  being  formed  at  one  place, 
and  is  disappearing  at  another,  that  clouds  change  their 
forms  so  readily.  No  one  who  has  watched  carefully  the 
forming  of  thunder  clouds  on  a  sultry  afternoon  can  doubt 
that  they  are  really  "springs"  of  water  vapor,  that  rise 
into  the  upper  air,  and  then  fall  again  in  great,  billowy 
masses. 

269.  Forms  of  Clouds. —  The  four  principal  forms  taken 
by  clouds  are  the  following: 

(1)  Cumulus  clouds  (Fig.  218);  these  are  so  called  from  the  word 
meaning  "a  heap,"  because  they  are  rounded  like  heaps  of  wool.     We 
have  the  same  meaning  in  the  word  "accumulate."     Cumulus  clouds 
are  formed  by  ascending  air  currents  laden  with  moisture.     They  are 
commonly  seen  on  warm  summer  afternoons,  at  a  height  of  one  to  five 
miles,  and  often  bring  on  thunderstorms  and  showers. 

(2)  Cirrus  clouds   (Fig.  219).     Cirrus  is  from  a  word  meaning 


FORMS   OF   CLOUDS 


239 


Fig.  218. 
Cumulus  Clouds.     Copyright,  International  Stereograph  Co. ,  Decatur,  111. 


Fig.  219. 

Cirrus  Clouds — "Mackerel  Sky."     Copyright,  International  Stereograph 
Co.,  Decatur,  111. 


240  THE  WEATHER 

"feather."  These  clouds  are  distinguished  by  the  distinct  lines  that 
make  them  up.  The  lines  may  be  arranged  in  many  strange  forms, 
such  as  plumes,  hazy  streaks,  etc.  Cirrus  clouds  are  the  highest 
clouds;  they  are  often  above  five  miles  high,  and  consist  of  minute 
particles  of  ice  or  snow.  One  arrangement  of  cirrus  clouds  is  called  a 
"mackerel  sky." 

(3)  Stratus  clouds;  these  are  so  called  because  they  occur  in  layers 
{cf.  §  286).     Stratus  clouds  are  lower  than  the  other  two;  usually  from 
half  a  mile  to  three  miles  high. 

(4)  Nimbus  clouds,  so  called  from  nimbus,  "  a  veil."    These  clouds 
are  cumulus  or  stratus  clouds  that  are  depositing  rain  or  snow. 

270.  Rain  and  Snow. —  When  the  particles  of  water 
mist  that  make  up  a  cloud  gather  together  into  drops, 
they  fall  into  the  air  below  the  cloud.     If  this  air  is  nearly 
saturated,  the  drops  continue  falling  until  they  reach  the 
earth  as  rain.     If  the  conditions  necessary  for  the  forma- 
tion of  raindrops  occur  below  0°  C.,  snow  flakes  will  be 
formed  (cf.  §  95,  Fig.  76). 

Cloudbursts.  If  the  ascending  currents  of  moist  air  are  very  strong, 
as  in  thunderstorms  and  tornadoes  (cf.  §§  277  and  278),  an  enormous 
quantity  of  water  may  be  accumulated  in  the  cloud.  When  this  falls, 
the  rain  is  called  a  cloudburst. 

271.  Hail. —  Hail  is  made  up  of  pellets  or  "stones"  of 
ice  and  snow  in  alternate  layers.     Hailstones  probably 
begin  in  the  freezing  of  raindrops  at  lower  levels.     These 
are  carried  upward  by  ascending  currents,  are  dropped 
downward,  and  are  then  carried  upward  again ;  this  treat- 
ment is  repeated  many  times.    Thus  the  hailstones  take 
on  layer  after  layer  of  covering,  until  they  become  too 
heavy  to  be  supported  longer,  and  fall  to  the  ground. 
Hail  does  a  great  deal  of  damage,  not  only  to  window 
panes,  but  also  to  fruit  trees  and  crops. 


RAINFALL 


241 


272.  Rainfall. —  Rain  is  caught  for  measurement  in  a 
rain  gauge  (Fig.  220).  This  is  really  a  funnel  with  a  long 
stem.  The  opening  of  the  funnel  has  exactly  10  times  the 
area  of  a  cross  section  of  the  stem,  so  that  Vio  of  an  inch 
of  rainfall  gives  a  depth  of  1  inch  in  the  stem.  The  greater 
depth  of  water  in  the  stem  makes  the  reading  more  accu- 
rate. Snow  is  estimated  as  rain,  the  snow  being  allowed  to 
melt.  About  10  inches  of  snowfall  equals 
1  inch  of  rain;  but  the  relation  is  not 
accurate  for  any  particular  case,  since 
snow  falls  in  so  many  different  degrees  of 
wetness. 

Scientists  have  found  that  there  are 
several  rules,  or  laws,  of  rainfall.  Among 
them  are  the  following: 

(1)  Rainfall  is  less  in  the  interior  of 
continents    than    on    the    coast.      The 

amount  for  each  continent  depends  on  how  far  rain 
clouds  can  penetrate  before  a  mountain  barrier  or 
plateau  condenses  their  moisture. 

(2)  The  greatest  rainfall  occurs  in  the  tropics.     This  is 
due  to  the  great  capacity  of  hot  air  for  moisture,  or,  better, 
to  the  great  evaporation  that  can  occur  at  high  tempera- 
tures. 

(3)  When  rainfall  takes  place  on  mountain  slopes,  the 
sides  get  more  than  the  base.     This  is  true  for  the  reason 
that  the  moist  air  currents  that  bring  the  rain  must  go  up 
a  certain  distance  before  they  are  chilled  enough  to  give 
their  greatest  deposits. 

Let  us  now  consider  some  illustrations  of  these  rules.     No  regions 
are  absolutely  rainless,  but  half  of  the  earth's  land  surface  gets  less  than 


I     Receiv 
Funru 

1 

H 

/ 

Gauge- 

Fig.  220. 
Rain  Gauge. 

242 


THE  WEATHER 


EXERCISES  243 

20  inches  of  rain  in  a  year,  and  is,  therefore,  considered  unfit  for  farm- 
ing without 'irrigation  (cf.  §§42  and  297).  The  rainfall  in  Florida  and 
on  the  Gulf  coast  is  over  60  inches  a  year.  The  sea  coast  of  the  state 
of  Washington  has  up  to  100  inches.  These  abundant  rains  are 
brought  by  warm,  moist,  ocean  winds,  which  are  cooled  as  they  pass 
over  the  land.  In  the  Plains  Region,  just  east  of  the  Rocky  Mountains, 
the  annual  rainfall  is  below  20  inches;  in  the  Nevada  Desert,  just  east 
of  the  Sierras,  it  is  less  than  5  inches. 

The  most  wonderful  rainfall  in  the  world  is  in  India,  where  the 
average  is  500  inches  a  year.  This  enormous  amount  is  brought  by 
the  southwest  winds  (monsoons)  from  the  heated  Indian  Ocean,  as 
they  ascend  the  land  to  the  tops  of  the  Himalayas.  Beyond  the 
mountains  the  monsoon  is  a  dry  wind,  and  the  plateau  of  Thibet,  over 
which  it  passes,  is  largely  a  desert. 

273.  Exercises. 

1.  Does  the  color  of  the  soil  have  anything  to  do  with  the  amount 
of  heat  it  can  absorb?    Why  does  the  snow  under  specks  of  dirt  melt 
more  rapidly  than  the  clean  snow  beside  it?    Why  does  snow  under  a 
heap  of  dirt  melt  so  slowly? 

2.  Why  does  a  high  mountain  top  exposed  to  the  sun  become  very 
much  hotter  in  the  daytime  than  land  in  the  valleys,  but  at  night  very 
much  colder? 

3.  A  balloon  that  is  at  a  certain  height  during  the  night  usually 
takes  a  sudden  leap  skyward  at  sunrise.     Explain  why. 

4.  Why  does  covering  a  plant  at  night  prevent  it  from  being  frost- 
bitten? 

5.  Would  you  feel  any  wind  if  you  were  in  a  region  from  which  an 
air  current  was  ascending?    Why? 

6.  Why  is  the  seashore  of  a  country  cooler  in  summer  and  warmer  in 
winter  than  the  interior? 

7.  Suppose  that  air  containing  moisture  rises  and  expands  until  it 
is  cooled  below  the  dew  point;  what  effect  does  the  condensing  of  its 
moisture  have  upon  its  temperature  (cf.  §  70)? 

8.  Suggest  why  a  fog  is  formed  more  readily  in  a  smoky  atmosphere 
than  in  a  clear  one. 


244 


THE  WEATHER 


9.  When  you  blow  your  breath  into  a  cold  glass  bottle  or  lamp 
chimney,  you  form  a  deposit  of  dew  on  the  inside.  Why?  How  cold 
must  the  condensing  object  be? 

10.  Under  what  conditions  can  you  " see  your  breath"?    Why  does 
the  condensed  moisture  disappear? 

11.  Find  out  how  large  a  hailstone  may  become. 

12.  If  a  dish  containing  a  mixture  of  salt  and  ice  is  left  outside  on  a 
cold  day,  it  gathers  little  if  any  frost;  but  when  it  is  brought  into  a 
warm  room,  it  condenses  a  great  deal.    Why? 

13.  Clouds  are  often  formed  on  the  headland  shown  in  Fig.  107, 
§  132,  which  travel  with  the  wind  (horizontally)  a  short  distance,  and 
then  disappear.    Why  are  the  clouds  formed?    Why  do  they  disappear? 

14.  There  is  a  steep  ascent,  in  the  form  of  hills  or  mountains, 
practically  the  entire  distance  around  the  coast  of  Australia.    Would 
you  expect  the  interior  to  be  dry  or  moist?    What  are  the  facts  regard- 
ing Australia? 

274.  The  Winds. —  The  cause  of  winds  is  the  inequal- 
ities of  atmospheric  pressure.  The  air,  being  gaseous, 
has  great  freedom  of  motion;  so  that,  if  the  pressure  be- 
comes low  at  any  given  place,  the  surrounding,  heavier 
air  crowds  in  from  all  sides,  and  buoys  the  lighter  air 
upward.  These  horizontal  currents  are  the  winds. 

A  fire,  burning  in  the  open  air  on  a  still  day  (Fig.  222),  illustrates 

^ admirably  the  origin 

of  winds.  The  warm 
air  and  smoke  are 
carried  upward  to  a 
certain  level,  and  then 
spread  out  horizon- 
tally. At  some  dis- 
tance they  return  to 
the  earth,  and  move 
toward  the  fire  as 
strong  drafts.  The 


FIRE 


Fig.  222. 
The  winds  are  fomed  like  the  currents  about  an  open  fire. 


REGULAR   WINDS  245 

horizontal  currents  at  the  earth's  surface  are  the  only  parts  of  this 
circulation  that  we  ordinarily  notice,  but  there  are  always  horizontal 
currents  at  higher  levels,  flowing  in  the  opposite  direction;  and  there 
are  downward  currents  to  balance  the  ascending  ones. 

The  force  with  which  the  wind  will  blow  toward  any 
given  place  depends  upon  the  difference  in  atmospheric 
pressure  between  that  place  and  the  region  about  it. 
Thus,  if  the  barometer  pressure  at  one  place  (A)  on  a 
horizontal  plain  is  29.9  inches,  and  if  two  neighboring 
places  (B)  and  (C)  have  pressures  of  29.8  inches  and  29.7 
inches,  respectively,  the  velocity  of  the  wind  from  A  to  C 
will  exceed  that  from  A  to  B,  or  from  B  to  C.  We  should 
expect  this  to  be  so,  since  we  know  that  water  will  flow 
more  rapidly  down  a  steep  incline  than  down  a  gentle  one. 

We  can  gather  these  facts  together  in  one  law  of  the 
winds: 

The  winds  blow  because  of  the  force  of  gravity,  and  always 
from  a  region  of  high  barometer  pressure  to  one  that  is  low. 
The  velocity  of  the  wind  is  greatest  where  the  change  of 
pressure  is  the  most  abrupt. 

The  instrument  by  which  we  measure  the  velocity  of  the  wind  is  the 
anemometer  (pronounced  an-e-mfan'-e-ter;  the  word  is  from  anemos, 
"wind,"  and  meter,  "measure")-  It  is  a  windmill  with  hollow,  cup- 
shaped  sails;  the  speed  with  which  it  revolves  is  registered  on  a  dial  as 
so  many  miles  per  hour.  A  light  wind  has  a  speed  of  less  than  10  miles 
an  hour;  it  can  just  move  the  leaves  of  trees.  A  high  wind,  blowing  at 
25  to  40  miles  an  hour,  sways  the  trees  themselves.  In  a  gale  the  wind 
is  over  40  miles  an  hour;  in  a  hurricane  or  a  tornado  (cf.  §§  278  and  279) 
it  is  above  60  miles,  and  may  reach  200  or  more. 

275.  Regular  Winds. —  On  the  land,  the  unevenness  of 
the  surface  and  the  different  degrees  of  heating  and  cool- 
ing at  different  places  produce  variable  winds;  but  the 


246  THE  WEATHER 

ocean  furnishes  a  free,  unbroken  path  for  air  currents; 
hence  winds  that  blow  over  the  ocean  often  keep  their 
direction  for  weeks  and  months  at  a  time.  Such  regular, 
long-continued  winds  are  the  trade  winds  of  temperate 
latitudes,  and  the  monsoons  of  the  Indian  and  West 
Pacific  oceans  (cf.  §  272). 

Land  and  sea  breezes  are  also  regular  winds,  due  to  the 
alternation  of  day  and  night.  By  day,  the  air  over  the 
land  is  warmed  more  than  the  air  over  the  water.  Con- 
vection currents  are  thus  set  up  on  the  land,  which  cause 
an  inflow  of  air  from  the  ocean  —  the  sea  breeze.  At 
night  the  land  cools  more  rapidly  than  the  ocean,  and  as 
a  result  the  ascending  air  current  is  over  the  water, 
hence  there  is  a  flow  of  air  from  the  land  —  the  land 
breeze. 

276.  Cyclones.—  If  the  earth  were  not  rotating  on  its 
axis,  winds  would  blow  toward  the  area  of  low  pressure 
as  directly  as  possible,  in  straight  lines,  as  the  spokes  of 
a  wheel  come  together  at  the  hub.  But  the  rotation  of 
the  earth  causes  the  air  to  flow  toward  the  ' l  low  "  area  by  a 
curved  route.  As  a  result  of  the  curved  paths  of  the 
winds,  the  air  at  the  center  is  set  in  a  whirl.  A  dust 
whirlwind  illustrates,  on  a  small  scale,  this  circular  move- 
ment of  air;  a  cyclone  is  a  great  whirl  that  may  be  1,000 
miles  in  diameter  and  5  miles  high. 

In  the  northern  hemisphere  the  direction  of  this  whirl- 
ing mass  of  air  is  opposite  that  of  the  hands  of  a  clock.  If, 
in  this  hemisphere,  you  stand  with  your  back  to  the  wind, 
the  center  of  low  pressure  will  be  towards  the  left.  In  the 
center  of  the  cyclone  there  is  comparative  calm. 


THUNDERSTORMS 


247 


B 


The  whole  area  of  low  pressure  moves  in  a  definite 
direction.  In  the  northern  United  States  this  direction 
is  easterly;  the  cyclones  begin  in  western  Canada.  The  ve- 
locity of  the  eastward  movement  is  about  30  miles  an  hour. 

Cyclones  must  not  be  confounded  with  tornadoes  (cf. 
§  278),  which  are  smaller  masses  of  very  rapidly  revolving 
air,  and  which  do  great  damage.  True  cyclones  bring 
the  cold  waves  that  sweep  down  upon  us  at  more  or  less 
regular  intervals,  both 

in  summer  and  in  win-  ^ /     NN 

ter,  dissipating  the  ex-  /  \ 

hausted  air,  and  giving  //  ^ 

vigor  to  our  people. 

The  curved  path  taken  by 
the  wind  in  approaching  a 
"low"  area  is  simply  the 
result  of  two  motions ;  one  is 
the  straight-line  motion  of 
the  wind,  by  which  it  seeks 
the  "low";  the  other  is  the 
rotation  of  the  earth  from 
west  to  east.  The  path  of  a 
person  on  a  revolving  bridge 
(Fig.  223)  can  be  made  to 

illustrate  the  effect  of  these  two  motions.  Suppose  that  the  bridge  is 
standing  still,  and  that  you  walk  toward  a  street  car  at  the  opposite 
end;  your  path  is  a  straight  line.  But  suppose  that  the  bridge  turns, 
while  you  continue  to  walk  toward  the  car.  Your  path  on  the  bridge 
will  change  its  direction  at  every  point:  it  will  be  a  curve. 

277.  Thunderstorms. —  Thunderstorms  are  smaller 
disturbances  in  the  great  cyclones;  the  frictional  electricity 
(lightning)  that  comes  with  them  (cf.  §  147)  is  generated 
by  the  rapid  condensation  of  water  vapor.  The  cause  of 


Fig.  223. 

If  you  walk  across  a  revolving  bridge,  keeping 

your  direction  toward  some  object  on  the 

opposite  shore,  your  path  will  be 

curved,  somewhat  like  AC. 


248  THE  WEATHER 

the  condensation  is  an  ascending  column  of  warm  air 
loaded  with  moisture.  When  this  has  produced  a  large 
cloud  (cf.  §  269),  rain  falls,  and  cools  the  ascending  col- 
umn below  the  temperature  of  the  warm,  moist  air  that 
rises  around  it.  The  central,  ascending  column  thus 
becomes  a  cool,  descending  one,  which  draws  down  into 
it  the  wet  ascending  currents,  and  precipitates  their 
moisture  in  violent  rains.  The  thunderstorm  has  a  center 
of  high  pressure  and  low  temperature;  its  circumference 
has  a  low  pressure  and  a  high  temperature. 

278.  Tornadoes. —  Tornadoes,  or  "twisters,"  are  small 
cyclones,  as  distinguished  from  the  great,  but  not  violent, 
cyclonic  storms  (cf.  §  276).  But  while  the  tornado  is  of 
small  size,  it  is  very  violent  and  destructive.  The  wind 
sometimes  reaches  a  velocity  of  200  miles,  or  more,  an 
hour,  and  no  objects  on  the  earth  can  resist  it.  Heavy 
boulders  are  carried  away  hundreds  of  feet,  and  locomo- 
tives are  lifted  from  the  rails.  So  great  is  the  force  of  the 
wind  that  frail  objects,  such  as  twigs  and  straws,  are 
driven  into  oak  wood. 

A  tornado,  as  seen  approaching,  is  a  funnel-shaped  cloud  with  the 
small  end  downward.  The  lower  end  dangles  along  the  ground  in  an 
irregular  way,  touching  it  here  and  there.  The  path  of  the  tornado 
may  be  50  feet  to  half  a  mile  wide.  The  whole  storm  moves  north- 
easterly, in  the  northern  hemisphere,  at  a  rate  of  25  to  40  miles  an  hour; 
it  generally  exhausts  itself  in  an  hour  or  so. 

In  the  great  deserts,  large  whirlwinds  carrying  columns  of  sand 
continue  for  hours  at  a  time.  Waterspouts  are  tornadoes  over  bodies 
of  water.  Waterspouts  at  sea  precipitate  fresh  water.  This  fact 
shows  that  while  a  small  column  of  water  may  be  pushed  up  by  atmos- 
pheric pressure  (cf.  §  40)  toward  the  low  pressure  region  of  the  water- 
spout, most  of  the  water  in  the  waterspout  comes  from  the  air  itself. 


WEATHER  SERVICE  OF   THE   UNITED  STATES        249 

279.  Hurricanes. —  In  the  tropical  part  of  the  Atlantic, 
north  of  South  America,  violent  storms  are  developed, 
called   hurricanes.     Similar   storms  in   the   Pacific    and 
Indian  oceans  are  called  typhoons.     Both  are  great  whirl- 
ing masses  of  air,  with  a  diameter  of  300  miles  or  more, 
in  which  the  violence  of  wind  and  rain  becomes  enormous. 
The  "West  India"  hurricanes  move  northwestward  until 
they  reach  the  southeastern  coast  of  the  United  States; 
then  they  move  in  a  northeasterly  direction,  and,  finally, 
out  into  the  Atlantic.     They  usually  come  in  the  months 
of  July  to  October,  inclusive. 

At  the  approach  of  a  hurricane  or  typhoon,  the  sea  and  the  air  are 
calm,  and  the  barometer  falls.  Then  the  wind  begins  to  blow,  and 
clouds  and  rain  come  on.  The  velocity  of  the  wind  increases  to  that 
of  the  fiercest  gale,  or  even  to  that  of  a  tornado.  If  the  center  of  the 
hurricane  passes  over  a  ship,  the  sailors  notice  a  sudden  change  from 
black  darkness  and  the  most  violent  gale  to  a  dead  calm  and  a  clear 
sky.  The  barometer  will  now  be  very  low.  The  ship  is  in  the  "eye" 
of  the  storm,  an  area  perhaps  20  miles  in  diameter.  When  this  has 
passed,  the  wind  will  break  forth  again,  as  suddenly  as  it  stopped,  but 
it  will  be  from  the  opposite  direction.  Then  all  the  conditions  that 
were  noticed  when  the  storm  came  on  will  be  reversed  as  the  ship 
passes  out  of  the  storm  area. 

The  damage  to  shipping  and  to  life  because  of  hurricanes  is  very 
great,  both  in  the  West  Indies  and  in  the  southeastern  states.  It  is  not 
only  the  wind  and  rain  that  are  so  destructive,  but  also  the  great 
storm  waves  that  are  raised,  and  that  sweep  over  all  low-lying  islands 
and  coasts. 

Typhoons  are  still  more  extensive  than  hurricanes,  because  they 
have  a  greater  ocean  in  which  to  form  and  to  move. 

280.  Weather   Service   of   the   United   States.— The 
science  of  the  weather  is  called  meteorology  (pronounced 
me-te-or-ol'-o-gy).     A  Weather  Service,  or  Weather  Bu- 


250  THE  WEATHER 

reau,  is  especially  needed  in  the  United  States,  owing  to  the 
great  range  of  the  country  in  latitude  and  longitude,  and 
the  great  variety  of  its  weather  conditions.  The  Bureau 
is  a  part  of  the  Department  of  Agriculture. 

Many  trained  observers  gather  the  weather  conditions 
each  day,  at  8  A.  M.  on  the  Atlantic  coast  and  at  5  A.  M. 
on  the  Pacific.  When  their  reports  are  telegraphed  •  to 
Washington,  they  give  an  instantaneous  photograph  of 
the  weather  of  the  whole  country.  The  facts  reported  by 
the  observers  are  simply  the  barometer  height,  tempera- 
ture, rainfall  or  snowfall,  direction  and  velocity  of  the 
wind,  etc.  But  the  combined  results,  when  placed  upon 
a  map,  make  it  possible  for  the  expert  at  Washington  not 
only  to  tell  what  the  weather  is,  but  what  it  is  likely  to 
be.  Thus  the  coming  of  cold  waves,  of  storms  that  are 
likely  to  injure  ships,  of  floods  upon  rivers,  all  can  be  fore- 
told with  more  or  less  accuracy.  That  some  forecasts 
fail  does  not  mean  that  the  Weather  Service  is  at  fault, 
but  that  all  storms  are  not  alike.  But  the  forecasts 
actually  save  to  the  people  not  only  many  lives,  but 
millions  of  dollars'  worth  of  property  annually:  many 
times  the  cost  of  the  service. 

The  case  of  the  Mississippi  floods  illustrates  how  the  Service  works. 
If  there  are  heavy  rains  in  the  Upper  Mississippi  Valley,  there  will  be 
serious  floods  along  the  lower  course  of  the  river.  The  "  weather 
man"  knows  the  rainfall,  and  how  much  the  river  can  carry  off  in  an 
hour;  hence  he  knows  what  chance  the  river  has  of  carrying  all  the 
water  it  will  receive.  If  more  water  is  poured  into  it.that  it  can  carry, 
the  level  of  the  river  must  go  up.  The  greatest  floods  of  recent  years 
have  occurred  in  1897,  1903,  1912,  and  1913.  In  the  flood  of  1912  the 
Bureau  predicted  that  the  crest,  or  highest  part,  of  the  flood  would 
reach  54  feet  at  Cairo,  46  feet  at  Memphis,  53  feet  at  Vicksburg,  42 


WEATHER  MAPS  251 

feet  at  Baton  Rouge,  and  21.5  feet  at  New  Orleans.  The  results  agreed 
remarkably  with  the  predictions,  although  the  predictions  were  for 
floods  1  to  1 .5  feet  higher  than  any  previous  record.  Thus  warned,  the 
people  set  to  work  to  strengthen  the  banks  and  levees,  to  remove  their 
cattle  and  their  families  to  places  of  safety,  and  to  get  all  freight  away 
from  the  wharves.  It  is  estimated  that  property  to  the  value  of 
$16,180,000  was  saved  by  these  warnings.  The  cost  of  the  river  and 
flood  service  for  the  entire  country  during  1912  was  $80,000,  or  only 
Yl  of  1  per  cent  of  the  value  of  the  property  saved  in  this  one  flood. 

In  a  similar  way  the  Bureau  gives  warnings  of  coming  frost,  so  that 
whatever  is  possible  may  be  done  to  save  crops.  When  the  weather 
observer  notes  that  a  cold  wave  is  coming,  he  sends  word  to  the  prin- 
cipal city  of  his  region.  From  this  as  a  center,  warning  is  sent  by  tele- 
gram and  telephone,  by  messenger,  and  by  great  signs  placed  on  trains, 
to  all  the  producers  of  that  region. 

The  warning  which  the  Weather  Bureau  gives  to  shipping  is  also  of 
great  importance,  as  we  should  realize  if  we  could  count  the  many 
thousands  of  ships,  large  and  small,  that  annually  enter  and  leave  our 
ports  on  the  Atlantic,  the  Pacific,  the  Gulf,  and  the  Great  Lakes. 
Within  45  minutes  after  a  storm  is  predicted,  the  warning  is  placed  in 
the  hands  of  every  ship  captain  in  every  lake  and  ocean  port.  Storm 
'signals  are  also  put  up  in  all  ports.  As  a  result  of  the  Weather  Service, 
the  losses  due  to  storms  on  the  Great  Lakes  have  fallen  off  two  thirds. 


281.  Weather  Maps. —  In  the  preceding  section  we 
have  learned  how  useful  the  weather  service  is.  Let  us 
now  see  how  "weather  maps"  are  made.  In  the  first 
place,  all  the  weather  stations  having  the  same  barometer 
height  are  joined  by  solid  lines,  as  in  Fig.  224,  A.  These 
lines  therefore  show  equal  pressures,  and  are  called  isobars, 
from  isos,  "equal,"  and  barm,  "heavy."  If  we  examine 
the  map  we  shall  see  that  the  isobars  curve,  in  irregularly 
circular  lines,  about  areas  of  low  and  of  high  pressure. 
The  pressure  increases  from  the  centers  of  the  "lows"  to 


252 


THE  WEATHER 


WEATHER  MAPS 


253 


254 


THE  WEATHER 


SUMMARY  255 

the  centers  of  the  "highs."  The  "lows"  represent  cy- 
clonic storms,  and  the  "highs"  the  sharp,  bright  weather 
that  usually  follows  them. 

Figure  224,  A,  J5,  and  C,  are  complete  weather  maps,  as 
issued  by  a  local  weather  office.  They  show  the  isobars, 
and  also  the  isotherm  for  freezing;  that  is,  the  line  joining 
the  places  at  which  the  temperature  is  32°  F.  Note 
carefully  the  progress  of  the  "low"  from  March  13  to 
March  15,  and  also  the  effect  of  the  northwestern  "high" 
upon  the  isotherm  of  freezing.  These  maps  show  also  the 
temperature  of  individual  stations,  the  direction  of  the 
wind,  and  the  amount  of  rain  or  snow.  As  they  are 
issued,  they  contain  an  official  forecast  for  different  parts 
of  the  country. 

282.  Summary. —  The  " conditions  of  the  weather"  are  due  to  the 
properties  of  the  air  and  water  of  the  atmosphere. 

Ascending  currents  are  pushed  up  by  heavier  air,  which  is  pulled 
downward  by  gravity. 

A  given  volume  of  moist  air  is  lighter  than  an  equal  volume  of 
dry  air. 

An  ascending  air  column  is  an  area  of  low  pressure. 

About  70  per  cent  of  the  heat  received  from  the  sun  is  temporarily 
absorbed  by  the  earth.  The  lower  atmosphere  does  most  of  the  ab- 
sorbing. 

Air  is  cooled  by  its  expansion  as  it  rises,  and  is  heated  by  its  com- 
pression as  it  descends. 

When  a  given  volume  of  air  or  of  space  deposits  its  moisture  as 
rapidly  as  it  takes  up  new  moisture,  it  is  said  to  be  saturated  with 
moisture. 

The  humidity  of  air  is  the  weight  of  water  present  in  a  given  volume 
of  air. 

Relative  humidity  is  the  amount  present  as  compared  with  what 
the  space  could  hold  if  it  were  saturated. 


256  THE  WEATHER 

The  dew  point  is  the  temperature  at  which  air  is  just  saturated  with 
moisture. 

Frost  is  formed  when  the  dew  point  is  below  0°  C.  It  is  not 
frozen  dew. 

Clouds  are  fogs  "  up  in  the  air."  A  cloud  is  limited  to  the  region  in 
which  water  vapor  can  be  condensed  more  rapidly  than  the  condensed 
moisture  can  evaporate. 

Clouds  are  distinguished,  according  to  their  form,  as  cumulus,  cirrus, 
stratus,  and  nimbus  clouds. 

Rain  occurs  when  water  mist  collects  in  drops  that  reach  the  earth. 

Snow  is  formed  when  rain-forming  conditions  occur  below  0°  C. 
It  is  not  frozen  rain. 

Hail  usually  has  ice  and  snow  in  alternate  layers. 

Rainfall  is  measured  by  a  rain  gauge. 

The  mean  annual  rainfall  of  the  United  States  varies  from  a  few 
inches  in  the  deserts  up  to  100  inches  in  the  state  of  Washington. 

The  circulation  that  forms  the  winds  includes  horizontal  currents 
at  higher  levels  as  well  as  at  the  earth,  and  downward  as  well  as  upward 
currents. 

Winds  blow  in  curved  paths  toward  regions  of  low  pressure.  The 
velocity  of  winds  is  measured  by  the  anemometer. 

Regular  winds  are  trade  winds  and  land  and  sea  breezes. 

Cyclones  are  great  whirlwinds  in  the  air.  They  bring  our  "cold 
waves,"  but  are  usually  not  destructive.  In  the  northern  hemisphere 
they  revolve  in  a  direction  opposite  to  that  of  the  hands  of  a  clock. 

The  curved  path  of  the  air  in  cyclones  is  due  to  its  motion  in  straight 
lines,  together  with  the  rotation  of  the  earth. 

A  thunderstorm  has  a  center  of  descending  air  (high  pressure),  which 
draws  into  it  ascending,  moist  air. 

Tornadoes  are  small  cyclones  of  great  violence. 

Waterspouts  are  tornadoes  over  bodies  of  water. 

Hurricanes  and  typhoons  are  violent  cyclones  formed  in  the  tropics. 

Meteorology  is  the  science  of  the  weather. 

The  Weather  Service  of  the  United  States  collects  the  data  regard- 
ing the  weather,  and  from  them  constructs  daily  weather  maps.  From 
these  it  forecasts  cold  waves,  floods,  and  storms,  so  that  their  harmful 
results  may  be  avoided  as  far  as  possible. 


EXERCISES  257 

283.  Exercises. 

1.  Clouds  often  move  in  a  direction  exactly  opposite  to  that  of  the 
prevailing  wind;  what  may  be  the  explanation  (cf.  §  274)? 

2.  What  is  a  weather  vane?    Its  shape?    Why  has  it  this  shape? 
Why  does  a  windmill  (cf.  §  210)  often  have  a  vane? 

3.  Fishermen  on  the  sea  coast  often  sail  out  to  the  fishing  grounds 
at  or  before  daybreak,  and  return  about  noon.     Do  the  land  and  sea 
breezes  help  them,  or  hinder  them? 

4.  Suppose  that  a  cyclone  is  5  miles  high,  and  has  a  diameter  of 
1.000  miles;  how  many  times  its  height  is  its  diameter?     If,  to  show 
these  proportions,  I  make  a  circle  out  of  wooden  boards  one  inch  thick, 
how  many  inches  in  diameter  must  the  circle  be?    How  many  feet? 

5.  If  you  were  watching  a  barometer  while  a  thunderstorm  was 
passing,  what  change  in  its  height  would  you  observe  as  the  center 
reached  you?    What  would  you  observe  in  the  case  of  a  tornado? 

6.  Would  your  house  be  more  likely  to  collapse  inward,  or  outward, 
if  a  tornado  were  to  pass  near  it? 

7.  What  kind  of  an  air  current  do  you  think  there  is  at  the  "eye" 
of  a  hurricane? 

8.  In  narrow  bays  a  strong  wind  often  " piles  up"  the  water  several 
feet;  explain. 

9.  Find  out,  if  possible,  what  are  the  various  flags  used  as  weather 
signals. 

10.  In  what  ways,  in  addition  to  making  weather  predictions,  does 
the  Government  seek  to  prevent  loss  of  life  and  property  at  sea  and 
on  the  lakes?  What  recent  invention  has  been  of  great  assistance? 


CHAPTER  XIV 

ROCKS  AND  SOIL 

284.  The  Earth's  Crust. —  We  have  already  learned 
(cf.  §  38,  Fig.  30)  about  the  four  parts  that  appear  in  a 
cross  section  of  the  earth.     The  crust  is  merely  that  por- 
tion of  the  core  that  is  known  to  us;  so  far  as  we  know,  the 
core  contains  the  same  materials  as  the  crust,  but  in  a 
more  compact  form. 

If  we  examine  the  crust,  as  it  is  exposed  in  a  railroad 
cut,  a  cellar  excavation,  or,  best,  in  a  quarry  or  gorge,  we 
find  that  it  consists  of  two  parts : 

(1)  The  surface  materials,  or  mantle  rock; 

(2)  Bedrock. 

Mantle  rock  is  made  up  of  such  materials  as  clay,  sand, 
gravel,  and  pebbles,  all  of  which  are  usually  loose  enough 
to  be  worked  by  the  spade  and  the  pick.  That  upper 
portion  of  the  mantle  rock  which  we  can  use  for  growing 
crops  is  called  soil. 

Ordinary  excavations  may  not  be  deep  enough  to  go 
through  the  mantle  rock;  but  everywhere,  and  at  only  a 
moderate  depth,  the  mantle  stops,  and  we  have  bed  rock. 
When  bed  rock  is  exposed  at  the  surface,  we  have  an 
outcrop. 

285.  Some  Common  Rocks. —  Bed  rock  usually  con- 
sists of  fragments  of  some  mineral  or  minerals  (cf.  §  102) 
cemented  together.     The  cementing  material  hardens,  of 

258 


SOME  COMMON  ROCKS  259 

"sets,"  around  and  between  the  fragments,  much  as  lime- 
stone holds  sand  together  in  mortar. 

The  most  common  rocks  are  sandstone  and  limestone. 
In  sandstone,  fragments  of  sand  (quartz)  are  cemented  by 
iron  oxide  or  silicic  (pronounced  sil-is'-ik)  acid.  Lime- 
stone usually  consists  of  masses,  sometimes  very  small, 
having  the  shape  of  shells  and  the  hard  parts  of  water 
animals.  These  are  compact,  and  cemented  together  by 
calcium  carbonate.  Animal  and  plant  remains,  as  we 
find  them  in  rocks,  are  called  fossils. 

When  the  cementing  materials  of  a  rock  are  removed, 
the  rock  falls  into  its  fragments.  Sandstones  are  often 
found  that  can  be  crumbled  in  the  hand,  owing  to  the 
loss  of  cementing  material. 

Shale  is  a  soft  rock  that  splits  easily  into  thin  leaves. 
It  is  made  of  flattened  particles  of  clay,  with  cementing 
material. 

Granite  consists  of  four  minerals :  quartz,  feldspar,  mica, 
and  hornblende.  Quartz  looks  like  glass,  but  is  harder. 
It  crystallizes  in  hexagonal  forms  (cf.  Fig.  75,  §  95).  In 
granite  it  forms  small,  shiny  masses.  The  feldspar  of 
granite  is  usually  pink  or  white.  The  mica  forms  shiny 
masses  that  can  be  split  off  in  very  thin  leaves  (cf.  §  250). 
The  hornblende  usually  exists  as  black  crystals. 

The  most  easily  attacked  of  the  ingredients  of  granite 
is  feldspar;  the  carbonic  acid  of  rain  water  decays  it.  So 
the  granite's  quartz  becomes  sand,  and  its  feldspar  be- 
comes clay. 

Conglomerate  is  a  gravel  of  various  materials  cemented 
together. 

We  have  artificial  rocks  as  well  as  natural  ones.    In  making  articles 


260 


ROCKS  AND  SOIL 


out  of  artificial  stone,  men  shape  the  rock  material  while  it  is  soft  and 
plastic,  and  then  bake,  or  "fire"  it.  The  people  of  ancient  Babylonia 
and  Assyria  made  their  ordinary  records,  such  as  notes,  deeds,  and 
mortgages,  as  well  as  the  records  of  their  history  and  literature,  upon 
clay  tablets,  and  then  baked  the  clay  in  the  sun. 

Earthenware  articles,  such  as  bricks,  jars,  and  tiles,  are  made  of 
•common  clay,  hardened  by  heat.  If  salt  is  put  into  the  heating  furnace 
(kiln),  the  articles  receive  a  glazed  surface. 

Porcelain  and  china  are  obtained  by  the  " firing"  of  a  mixture  of 
kaolin  (a  pure,  white  clay),  quartz,  and  feldspar.  The  feldspar  melts 
first,  and  cements  the  mixture  together.  The  first  " firing"  of  porce- 
lain and  china  articles  takes  place  at  a  rather  low  temperature ;  then  the 

glaze  is  added  to  the  surface, 
and  the  article  is  heated  to  a 
high  temperature,  often  for 
several  days. 

Stoneware  is  much  like  por- 
celain, but  it  has  not  been 
heated  to  so  high  a  tempera- 
ture. As  a  result,  it  is  opaque, 
while  porcelain  is  translucent. 
The  science  of  making  articles 


out  of  artificial  stone  is  called 
keramics. 

Concrete  is  another  artifi- 
cial stone,  made  out  of  cement, 
gravel,  and  water.  The 
cement  and  the  water  unite, 
and  cause  the  mixture  to 
"set."  Cement  is  formed  by 
the  heating  of  a  mixture  of 
limestone  and  clay. 


Fig.  225. 

Niagara   Falls   are  being  undermined   all  the 
time,  because  the  soft  shale  is  being  worn 
away  by  the  water,  and  the  hard  lime- 
stone falls  into  the  Gorge.     From 
Hopkins,  after  Gilbert. 


286.  Classes  of  Rocks. —  If  we  examine  many  different 
rocks,  we  shall  find  that  we  can  divide  them  into  two  great 
classes.  One  consists  of  rocks  having  a  more  or  less 


CLASSES  OF  ROCKS 


261 


definite  layer  structure.  A  cross  section,  especially  when 
polished,  shows  multitudes  of  parallel  lines.  These  rocks 
are  of  different  materials,  a  layer  of  one  material  covering 
a  layer  of  another  material.  Thus,  the  rock  under  the 
Niagara  River,  at  the  Falls,  is  a  hard  limestone  (Fig. 
225).  This  rests  upon  a  layer  of  soft  shale.  Sandstone 
also  forms  one  of  the  layers. 

Each  set  of  layers  of  rock  of  one  kind  is  called  a  stratum. 
The  plural  is  strata.  Rocks  made  up  of  strata  are  called 
stratified  rocks  (cf.  §  132, 
Fig.  107).  They  were 
deposited,  as  sediment, 
under  water;  hence  they 
are  also  called  aqueous 
rocks,  and  sedimentary 
rocks.  Limestone,  sand- 
stone, shale,  and  con- 
glomerate are  stratified 
rocks. 

Granite  does  not  have 
this  layer  structure,  and 
belongs  to  the  class  of 
unstratified  rocks.  The 
minerals  present  in  gran- 
ite are  crystallized  in 
separate  masses,  and  the 

masses  are  closely  interlaced.  This  is  what  we  should 
expect  if  quartz,  feldspar,  etc.,  had  been  melted  together, 
and  then  allowed  to  cool  very  slowly. 

Other  common  unstratified  rocks  are  basalt,   lava,   and  pumice. 
Basalt  (Fig.  226)  is  often  called  ' '  trap  rock."     Lava  and  pumice  have  a 


Fig.  226. 

Giant's  Causeway,  Ireland;    Made  of  Basalt. 

Copyright,  The  international  Stereograph 

Co.,  Decatur,  111. 


262  ROCKS  AND  SOIL 

structure  like  glass,  and  show  no  crystals.  Slag  is  an  artificial  unstrati- 
fied  rock  (cf.  §  119,  Fig.  94).  Since  unstratified  rocks  were  probably 
in  a  melted  condition  when  deposited,  and  therefore  hot,  they  are  often 
called  igneous  rocks,  from  the  Latin  ignis,  "fire." 

Marble  is  an  example  of  a  third  class  of  rocks.  Marble 
is  calcium  carbonate,  like  limestone;  but  instead  of  show- 
ing a  layer  structure,  it  is  crystalline,  like  igneous  rocks. 
We  believe  that  such  rocks  were  originally  stratified,  but 
that  they  have  been  changed  by  heat  and  pressure.  They 
are  called  altered,  or  metamorphic  rocks.  Anthracite 
€oal  is  metamorphic  coal,  and  slate  is  metamorphic  shale. 
Often  all  the  stages  in  the  change  from  stratified  rocks  to 
apparently  igneous  rocks  can  be  seen. 

287.  Origin  of  Stratified  Rocks. —  In  the  preceding 
section  we  learned  that  stratified  rocks  were  formed  as 
sediment,  under  water,  while  igneous  rocks  were  formed 
by  the  cooling  of  melted  minerals.  How  do  we  know  this? 

The  best  method  of  finding  out  how  changes  took  place 
in  the  past  is  to  study  the  changes  taking  place  to-day. 
We  know  that  running  water  can  carry  sediment,  and  that 
when  a  stream  empties  into  a  body  of  water,  such  as  a 
lake  or  pond,  its  velocity  is  checked,  and  it  deposits  its 
sediment  in  more  or  less  horizontal  layers. 

Imagine  a  small  stream  emptying  into  a  quiet  pond.  After  a  rain 
the  swollen  stream  will  bring  down  mud,  sand,  and  often  fine  gravel. 
When  it  enters  the  pond,  it  drops  its  sediment,  the  largest  particles 
first,  and  the  smallest  ones  last.  The  finest  particles  take  a  long  time 
to  settle,  and  are  spread  out  over  the  bottom  of  the  pond.  Then,  after 
a  while,  another  rain  comes,  and  a  second  deposit  is  placed  over  the 
first  one.  The  largest  particles  of  the  second  deposit  will  be  on  top  of 
the  finest  particles  of  the  first.  In  this  way  the  sediment  will  take 
on  a  layer  structure,  and  a  vertical  cross  section  of  it  will  show  the 


ORIGIN  OF  IGNEOUS  AND  METAMORPHIC  ROCKS     263 

fine,  parallel  lines  that  are  present  in  stratified  rock.  If  now  the 
sediment  were  to  become  very  thick,  producing  great  pressure  on  the 
lowest  layers,  and  if  a  cementing  material  were  present,  the  clay  de- 
posited in  the  pond  might  be  changed  to  shale,  and  the  sand  to  sand- 
stone. 


288.  Origin  of  Igneous  and  Metamorphic  Rocks. —  We 
cannot  observe  the  formation  of  igneous  rocks  as  easily 
as  that  of  stratified  rocks;  but  there  are,  even  now,  vol- 
canic regions  in  which  melted  rock  is  being  expelled  from 
the  interior  of  the  earth. 
Sometimes  the  melted 
rock  hardens  to  a  glassy, 
brittle  rock,  forming  ob- 
sidian and  lava  (Fig.  227). 
Sometimes  the  volcanic 
material  is  full  of  gas 
bubbles,  and  hardens  to 
form  pumice. 

New  England  has  no 
volcanic  conditions  to- 
day, but  there  is  every 
evidence  that  it  had  them  in  the  past ;  for  in  many  places 
great  dikes  of  igneous  rock  cross  its  other  rocks,  and  these 
are  nothing  but  rock  cracks  that  have  been  filled,  from 
below,  with  lava.  In  Oregon  great  areas  of  lava  are 
found  on  the  surface. 

Granite  differs  from  lava  and  other  igneous  rocks  in  that  it  seems  to 
have  been  pushed  into  cracks  and  pockets  entirely  beneath  the  earth's 
surface.  Its  minerals  must  have  crystallized  out  during  a  long  period 
of  very  slow  cooling.  When  we  now  find  granite  at  the  earth's  surface, 
we  believe  that  the  rock  which  once  covered  it  has  been  worn  away. 


Fig.  227. 

A  Roman  Mill;  Made  of  Lava.    Field  Museum 
of  Natural  History. 


264  ROCKS  AND  SOIL 

It  is  evident  that  we  must  think  of  igneous  rock  as  lying  under  all 
other  rocks.  Time  and  again  some  of  it  has  been  liquefied,  and  has 
penetrated  into  the  cracks  of  stratified  rocks,  or  has  overflowed  them. 
As  a  result  the  stratified  rocks  near  by  were  heated,  and  changed  in 
structure :  they  became  metamorphic. 

289.  Weathering  of  Rocks. —  The  earth's  solid  crust  at 
any  given  time  is  what  it  is  because  of  two  great  agencies : 
(1)  the  upbuilding  agencies,  and  (2)  the  down-tearing 
agencies.  It  is  as  though  you  were  to  set  one  man  at 
work  building  up  your  house,  and  another  man  at  tearing 
it  down.  The  size  and  shape  of  your  house  would  depend 
upon  the  rates  of  speed  at  which  the  two  men  worked. 
So  it  is  with  the  earth.  Agencies  are  at  work  building  up 
the  land:  igneous  rock  is  pushed  up  from  beneath,  and 
stratified  rock  is  formed  by  deposit.  But  no  sooner  is 
rock  brought  to  the  surface  than  it  is  attacked  by  the 
air,  by  the  surface  water,  and  by  plants  and  animals.  In 
this  way  bed  rock,  whether  stratified  or  igneous,  is 
changed  to  mantle  rock,  and  mantle  rock  to  soil;  then  soil 
is  carried  away  by  wind,  rain,  and  stream,  and  deposited 
as  sediment ;  the  process  of  rock  making  begins  over  again. 
The  action  of  air  and  of  the  "weather"  upon  the  crust  of 
the  earth  is  called  weathering. 

Illustrations  of  weathering  can  be  seen  wherever  rock  (or  any  mate- 
rial) is  exposed  to  the  air.  At  the  base  of  every  cliff  there  is  a  heap  of 
detritus,  or  talus,  that  has  been  broken  off  from  the  rock  above.  Around 
every  boulder  in  a  field,  if  the  ground  is  undisturbed,  you  can  find  chips 
and  dust  that  were  once  parts  of  the  boulder.  Polished  marble 
monuments  become  worn  and  rough,  and  limestone  walls  soon  have 
a  surf  ace  that  you  can  rub  off.  Artificial  weathering  is  shown  in  the 
wearing  off  of  stone  and  cement  sidewalks,  floors,  and  steps,  from 
constant  use. 


»       CAUSES  OF  WEATHERING  265 

290.  Causes  of  Weathering.— The  chief  agencies  of 
weathering  have  already  been  named  (cf.  §  289) ;  they  are 
air,  water,  plants,  and  animals.  Of  these,  air  and  water 
are  the  most  important.  Both  air  and  water  produce  (1) 
physical  changes  (cf.  §  98)  in  rock,  by  wearing  off  and 
carrying  away  rock  material;  and  (2)  chemical  changes, 
in  that  they  actually  alter  the  nature  of  the  minerals  of 
the  rock.  Thus  the  carbon  dioxide  and  water  of  the  air 


Fig.  228. 

Sand  Dune  Being  Carried  by  the  Wind  into  the  Grand  Calumet  River,  at 
Miller's,  Ind.     Negative  by  Geo.  D.  Fuller. 

(carbonic  acid;  cf.  §  126)  act  chemically  in  decomposing 
feldspar  (cf.  §  285),  in  converting  limestone  into  a  soluble 
compound  (cf.  §  132),  and  in  "dissolving"  the  cementing 
material  of  many  rocks,  thus  causing  the  rocks  to  crumble 
Air  can  also  act  chemically  upon  rocks  by  oxidizing  them 
as  it  does  iron  (cf.  §  48). 

We  see  the  air  (wind)  acting  as  a  mechanical,  or  physical,  agent  in 
carrying  off  dust,  and  in  moving  the  sand  of  a  sandbank,  or  dune,  and 


266  ROCKS  AND  SOIL 

so  shifting  the  whole  bank  (Fig.  228).  A  strong  wind  carrying  sand 
uses  the  sand  as  a  cutting  tool,  just  as  a  sand  blast  etches  glass  (cf.  §  43). 

Water  can  carry  along  much  larger  objects  than  air,  because  it  is 
denser.  Mountain  torrents  often  roll  down  great  boulders ;  but  usually 
a  river  carries  small  gravel,  sand,  and  the  still  finer  particles  that  make 
up  mud  and  clay  (cf.  §  287) .  And  just  as  wind  carrying  sand  sculptures 
rocks,  so  a  river  carrying  sediment  scours  out  its  bed. 

The  expansion  of  water  in  freezing  (cf.  §  70)  is  one  of  the  most  im- 
portant causes  of  weathering.  Most  rocks  are  porous,  and  all  have 
cracks.  When  water  freezes  in  the  rock,  the  rock  is  forced  apart. 
It  is  a  common  experience  that  fragments  fall  from  a  cliff  in  the  spring, 
when  we  have  frequent  freezes  and  thaws,  and  when  the  frozen  water 
in  the  rock  crevices  melts,  and  releases  the  portions  broken  from  the 
cliff. 

Plants  have  already  been  named  as  causes  of  weathering.  The 
decay  of  plants  gives  acids,  and  these  attack  rock  (cf.  §§  132  and  217). 
Plant  roots  also  act  mechanically,  tearing  rocks  apart,  much  as  a  tree 
root  breaks  a  sidewalk. 

291.  Drift. —  What  is  the  origin  of  mantle 'rock  and 
soil?  And  why  are  soils  so  different?  We  have  answered 
these  questions  partly  in  our  study  of  weathering.  Mantle 
rock  and  soil  are  decayed  bed  rock.  But  in  this  country 
we  find  the  mantle  related  to  its  bed  rock  in  two  entirely 
different  ways.  In  our  southern  states  (except  in  the 
Gulf  Region)  the  mantle  rock  and  the  bed  rock  it  covers 
are  of  the  same  material.  As  we  dig  down  we  find  the 
rock  less  and  less  decayed,  until  we  come  to  bed  rock.  If 
there  are  boulders,  they  are  simply  harder  parts  of  the  bed 
rock,  which  have  not  decayed  as  rapidly  as  the  rest.  In 
such  a  case  we  must  believe  that  the  mantle  rock  was 
formed,  where  it  now  lies,  by  the  weathering  of  the  bed 
rock.  Mantle  rock  of  this  sort  is  called  residual  mantle 
rock  or  soil. 


DRIFT  267 

But  in  the  northern  states  the  mantle  is  usually  quite 
different  from  the  bed  rock  under  it.  Thus,  we  may  find 
a  mantle  of  sandy  soil  directly  over  limestone,  and  clay 
over  sandstone.  Moreover,  the  boulders  (and  there  are 
often  many  of  them)  are  of  materials  that  do  not  exist  in 
the  bed  rock  of  the  region  at  all,  but  must  have  been 
transported  from  a  great  distance.  All  mantle  rock  that 
has  been  brought  to  a  region,  and  not  formed  where  we 
find  it,  is  called  drift. 

The  agents  that  have  brought  drift,  like  the  agents  that  produce 
weathering,  are  Nature's  " common  workmen":  chiefly  air,  water,  and 
ice.  We  have  already  learned  that  the  wind  can  shift  a  great  sand 
bank  (cf.  §  290),  and  that  running  water  will  carry  away  material  from 
one  place,  and  then,  when  its  velocity  is  checked,  will  deposit  the 
material  at  another  (cf.  §§  287  and  290).  We  do  not  need  to  study 
rivers  to  learn  how  running  water  transports  and  deposits  materials; 
we  can  see  its  action  after  any  rain.  On  every  slope  the  rills  that  pour 
down  wear  away  the  earth,  and  form  grooves,  or  channels.  The 
transported  pebbles,  mud,  etc.,  are  deposited  at  the  base  of  the  slope. 
A  deposit  of  this  sort,  whether  brought  by  a  rill  or  by  a  great  river,  usu- 
ally takes  the  shape  of  the  Greek  letter  A  (our  D),  and  is  called  a 
delta.  The  "Gulf  Region"  of  this  country  is  largely  the  delta  of  the 
Mississippi. 

But  the  peculiar  drift  of  the  northern  states  (a  similar 
drift  is  found  in  Europe)  was  not  brought  by  air  or  by 
water;  we  have  abundant  evidence  that  it  was  brought  to 
its  present  position  by  a  great  sheet  of  ice,  which  covered 
the  land  for  a  time  as  the  interior  ice  sheet  now  covers 
Greenland.  The  ice  brought  fragments  of  igneous  rock 
from  Canada,  and  left  them  in  the  United  States.  It 
pushed  before  it  great  masses  of  clay  filled  with  stones  and 
boulders,  called  "boulder  clay,"  or  "till."  It  carried 
other  boulders  on  its  back.  By  means  of  great  stones 


268  ROCKS  AND  SOIL 

frozen  into  its  base  it  marked  the  bed  rock  with  grooves, 
so  that  the  direction  of  the  ice  streams  can  be  clearly 
traced.  The  time  during  which  the  ice  lasted  is  called 
the  Glacial  Period,  and  the  material  which  the  ice  brought 
with  it  is  called  glacial  drift. 

292.  Erosion. —  We  are  now  ready  to  give  a  name  to 
the  total  effect  of  the  weathering  process.     We  can  see 
that  the  land  is  everywhere  being  worn  down,  and  that 
the  material  formed  in  weathering  is  being  carried  by 
rains  into  the  rivers.     This  weathered  material,  together 
with  what  the  rivers  themselves  wear  away,  is  being  car- 
ried into  the  sea.     We  must  add  to  the  down-tearing 
agencies  the  action  of  the  sea  itself,  as  it  wears  away  the 
land  by  the  pounding  of  its  waves.     This  general  cutting 
down  of  the  land  level  we  call  erosion,  from  the  Latin 
rodeo,  "I  gnaw."     The  agents  of  erosion  are  air  and  water 
(including  ice) ;  they  owe  their  physical  energy  to  gravity, 
the  downward  pull  of  the  earth. 

293.  Exercises. 

1.  Is  soft  coal  a  rock?    To  which  class  does  it  belong?     How  was 
it  formed?     Cf.  §  118. 

2.  Remembering  that  shale  is  hardened  clay,  and  that  clay  "holds 
water,"  what  can  you  say  of  the  conditions  under  which  a  deposit  of 
coal  was  formed,  if  we  now  find  a  layer  of  shale  underneath  it? 

3.  Old  mortar  is  a  mixture  of  sand  and  limestone.     Which  is  the 
cementing  material?     How  can  you  remove  it  easily? 

4.  Why  is  sharp  sand  used  in  making  mortar?    Would  sand 
obtained  from  a  lake  beach  be  sharp? 

5.  How  do  pebbles  become  rounded?    If  you  find  a  bank  of  rounded 
pebbles  some  distance  from  any  body  of  water,  what  do  you  con- 
clude? 


SOIL  269 

6.  Glass  scratches  limestone,  and  is  scratched  by  quartz;  which  H 
the  hardest  of  these  three?     How  does  the  finger  nail  compare  with 
these  substances  in  hardness? 

7.  Suppose  that  the  rock  directly  under  the  Niagara  River  (Fig. 
225)  were  suddenly  to  become  a  soft  shale;  what  would  be  the  effect 
upon  Niagara  Falls?     Do  you  think  the  Falls  have  always  been  where 
they  are  now?     Why? 

8.  Compare  the  composition  of  granite  and  of  porcelain.     Which 
rock  may  be  called  the  cementing  rock  of  granite? 

9.  In  what  forms  besides  clay  tablets  did  ancient  peoples  leave  their 
records? 

294.  Soil. —  Soils  have  as  their  foundation  weathered 
rock.  Usually  this  is  a  mixture  of  sand  and  clay  (cf. 
§  285),  and  is  called  loam.  Besides  loam,  a  fertile  soil 
requires  humus,  or  vegetable  mould.  This  is  the  material 
formed  by  the  growth  and  decay  of  plants  and  trees;  we 
see  it  in  the  black  top-soil  of  a  forest.  Growing  plants 
need  humus  as  a  food;  but  it  is  more  than  this,  for  it  is 
the  means  by  which  the  minerals  of  the  loam  are  prepared 
for  the  use  of  the  plant.  The  subsoil  lies  below  the  culti- 
vated soil.  On  its  qualities  the  qualities  of  the  upper  soil 
depend. 

Soil  has  not  only  the  chemical  materials  of  loam,  humus, 
air,  and  water,  but  it  contains  multitudes  of  the  lower 
organisms,  such  as  bacteria  (cf.  §§56  and  324).  One  who 
studies  the  soil  carefully  soon  realizes  that  it  is  not  a  dead, 
inorganic  mixture,  but  a  world  of  life  and  activity.  He 
also  learns  that  a  fertile  soil  required  centuries  for  its 
development,  and  that  if  it  is  once  destroyed,  it  cannot  be 
restored  in  a  year  or  two.  Every  agriculturalist  needs  to 
know  what  his  soil  contains,  what  it  lacks,  for  what  crop 
it  is  suited,  and  how  it  ought  to  be  handled,  so  that  it  will 


270  ROCKS  AND  SOIL 

give  as  great  a  present  yield  as  possible,  without  losing  its 
fertility  for  the  future.  And  because  all  of  us,  no  matter 
where  we  live,  depend  upon  soil  products,  we  ought  all  to 
be  interested  in  the  soil  and  its  welfare. 

295.  Structure  of  Soil. —  We  can  classify  soils  as  to  the 
way  in  which  they  were  formed,  and  also  as  to  their 
structure.  A  sedentary,  or  residual,  soil  is  one  that  was 
formed  where  we  find  it  (cf.  §  291).  An  alluvial  soil  is 
one  formed  by  deposit  from  water.  Such  is  the  soil  of 
the  Gulf  Region  and  of  the  Nile  Valley.  Glacial  soils  are 
made  up  of  glacial  drift. 

Soils  that  are  very  sandy  are  called  light  soils.  They  are  easy  to 
cultivate,  and  they  absorb  water  easily.  But  they  also  lose  it  easily, 
so  that  their  plants  cannot  live  long  in  dry  weather.  Soils  with  an 
excess  of  clay  are  called  heavy  soils.  They  take  up  water  slowly;  but 
when  they  have  taken  it  up,  they  hold  it  very  firmly.  A  heavy  soil, 
on  level  ground,  and  in  a  region  of  good  rainfall,  is  likely  to  be  swampy. 
Such  soils  often  need  to  be  drained  by  the  digging  of  ditches  and  the 
laying  of  "  tiles,"  or  pipes.  If  heavy  soils  are  ploughed  while  too  wet, 
they  cake,  forming  large,  hard  lumps  separated  by  cracks. 

The  plant  gets  its  food  from  that  part  of  the  soil  that  is 
in  solution;  hence  a  soil  must  contain  water.  It  must  also 
contain  air  for  the  respiration  (cf.  §  52)  of  the  roots  and 
underground  stems.  For  these  and  other  reasons  the 
size  of  the  soil  particles,  and  the  distance  they  are  apart, 
are  of  great  importance  for  the  growing  of  crops.  Be- 
ginning with  the  largest,  we  may  classify  soil  particles  as 
gravel,  sand,  silt,  and  clay.  Dry  clay  particles  form  a 
dusty  powder,  like  flour.  From  a  soil  of  the  right  degree 
of  fineness  a  plant  can  draw  water  even  in  dry  weather, 
because  the  water  can  be  transferred,  by  capillary  action 


TILLING   THE  SOIL 


271 


(c/.  §  32),  from  the  place  having  more  water  to  the  place 
having  less.  Hence  the  effects  of  a  drouth  are  not  felt 
by  the  plant  for  a  long  time. 

Besides  the  water  that  is  held,  by  capillary  action, 
between  the  particles  of  the  soil,  each  minute  soil  particle 
has  a  film,  or  covering,  of  water,  which  it  does  not  lose 
entirely,  even  in  dry  weather.  This  water  film,  like 
capillary  water,  is  a  solution  containing  the  materials 
needed  by  growing  plants. 

296.  Tilling  the  Soil.— Tillage  is  the  working  of  the 
soil  by  the  use  of  implements.  The  implements  may  be 
simple  garden  tools,  such 
as  the  spade  and  hoe,  or 
they  may  be  plows,  culti- 
vators,  and  seeders, 
drawn  by  horses  or  en- 
gines. We  till  the  soil 
in  order  to  improve  its 
structure,  so  that  it  may 
retain  water  better,  and 
may  permit  plants  to  get 
their  nutriment  from  a 
wider  range.  We  also 
use  tillage  to  turn  under 
rubbish,  manure,  and 
fertilizers,  and  to  make 
them  part  of  the  soil.  Seeders  deposit  seeds  and  plants 
in  the  position  in  which  they  are  to  grow.  They  usually 
turn  the  soil  at  the  same  time. 

Plowing  (Fig.  229)  consists  in  forcing  a  slanting  knife  or  shovel,. 


Fig.  229. 

Egyptian  Pbwing.      Copyright,  International 
Stereograph  Co.,  Decatur,  111. 


272  ROCKS  AND  SOIL 

called  a  plowshare,  to  a  certain  depth  into  the  soil,  and  then  turning  the 
slice  of  soil  over  upon  itself  in  the  furrow.  The  slice  is  usually  laid  at 
an  angle  of  25°  to  50°  (half  a  right  angle  is  45°)  with  a  horizontal  plane, 
,so  that  the  edge  of  the  slice  projects  from  the  ground.  Plowing  not 
only  loosens  the  soil,  and  breaks  it  up,  but  it  also  brings  to  the  surface 
new  material  for  the  plant's  growth.  Modern  agriculture  has  greatly 
increased  the  depth  of  plowing,  as  well  as  its  extent.  Primitive  peoples 


Fig.  230. 
A  Disc  Plow.     The  whirling  discs  are  on  the  right.     Courtesy  of  Deere  and  Co. 

merely  scratched  the  surface,  and  were  able  to  till  only  a  limited 
area  of  land. 

Cultivating  is  shallow  plowing,  or  stirring,  of  a  soil,  usually  after  a 
crop  has  begun  to  grow.  Its  purpose  is  chiefly  to  keep  the  surface  soil 
in  a  powdered  condition,  so  that  it  will  retain  moisture.  Cultivating 
also  destroys  weeds.  In  dry  farming  frequent  cultivating  is  carried 
on;  this  produces  a  deep  dust  mulch,  or  covering,  which  prevents  the 
evaporation  of  water  from  the  surface,  and  yet  permits  moisture  to 
rise  from  the  subsoil  by  capillary  action. 

Plows  and  cultivators  are  of  many  types;  each  is  good  for  a  particu- 


IRRIGATION  273 

lar  kind  of  soil  and  a  particular  kind  of  work.  Disc  plows  (Fig.  230) 
have  a  revolving  cutting  instrument,  called  a  disc,  instead  of  a  plow- 
share. The  friction  is  less  than  with  an  ordinary  plow,  because  the 
cutting  tool  rotates  through  the  soil  instead  of  sliding  through  it  (cf. 
§  206). 

Gang  plows  consist  of  many  plowshares  attached  to  one  frame. 
They  can  be  used  on  large,  level  areas,  and  are  drawn  by  a  large  num- 
ber of  horses  or  by  engines  (tractors;  Fig.  231). 


Fig.  231. 

A  Gang  Plow.     This  one  has  ten  plowshares;  behind  it  is  a  cultivator. 
Courtesy  of  Deere  and  Co. 

297.  Irrigation. —  By  irrigation  we  mean  the  adding  of 
water  to  a  soil  to  make  up  for  a  lack  of  rain.  Irrigation 
may  be  carried  on  anywhere,  but  it  is  especially  im- 
portant in  desert  areas.  In  this  country  it  is  used  to 
supply  water  for  farming  and  fruit-raising  to  the  sections 
having  a  small  rainfall  (cf.  §§42  and  272).  Even  in 
almost  rainless  regions  there  is  usually  a  lake  or  stream 
that  has  a  large  amount  of  water  during  the  rainy  season, 
or  in  the  spring,  when  the  snows  melt  in  the  mountains. 
But  in  the  summer,  the  growing  season  of  crops,  there  is  no 
water.  Men  therefore  impound  the  water  in  large  reser- 


274  ROCKS  AND  SOIL 

voirs  at  the  time  there  is  an  abundance  of  it,  and  then  let 
it  run  off  slowly  during  the  dry  period.  Where  natural 
streams  are  wanting,  irrigation  canals  carry  the  water  from 
the  reservoirs  to  the  farms.  The  reservoir  is  made  by  the 
building  of  a  dam  across  the  outlet  of  a  lake,  or  at  some 
suitable  place  in  a  stream.  The  water  flowing  over  the 
dam  forms  an  artificial  waterfall,  which  is  often  used  for 
power  (qf.  §  162). 

There  are  several  methods  of  irrigation.  One  is  to  flood  the  land  to 
a  certain  depth,  and  then  to  allow  the  water  to  sink  into  the  soil.  The 
flooding  is  repeated  at  intervals.  Another  way  is  to  build  pipes  having 
openings  that  throw  sprays  of  water  over  the  land;  this  is  like  rain.  A 
third  way  is  to  have  furrows  for  the  water,  and  to  let  it  soak  sidewise 
into  the  growing  area. 

For  that  form  of  irrigation  which  we  call  " watering  the  garden" 
the  following  suggestion  is  excellent:  ''The  hose  should  be  used  in  a 
manner  to  resemble  rain.  Give  the  garden  a  good  soaking,  and  then 
let  it  alone  until  your  daily  observation  shows  you  that  it  has  dried 
out  to  a  depth  of  from  two  to  four  inches  from  the  top.  Then  repeat 
the  watering.  The  practice  of  frequent,  shallow  watering  is  wrong, 
as  it  induces  shallow  rooting;  when  the  watering  is  neglected,  the  roots 
near  the  surface  die,  and  the  plants  suffer.  If  a  garden  is  properly 
watered,  the  roots  will  go  down  some  distance;  if  watering  is  too  shal- 
low, they  will  run  along  horizontally,  just  under  the  top  of  the  ground. " 

298.  Fertility. —  The  fertility  of  a  soil  is  its  crop-pro- 
ducing power.  This  power  depends  upon  the  elements 
in  the  soil,  upon  the  physical  condition  of  the  soil,  upon 
the  water  supply,  and  upon  other  conditions.  None  of  the 
conditions  named  can  make  up  for  an  unfavorable  climate. 
A  soil  that  has  all  the  conditions  for  growing  corn  in  Iowa 
may  be  barren,  so  far  as  corn  is  concerned,  in  Labrador. 

It  seems  likely  that  at  least  10  chemical  elements  are 


LOSS  OF  FERTILITY  275 

taken  from  the  soil  by  plants;  hence  these  must  be  present 
to  make  a  soil  fertile.  Other  elements  are  needed  too, 
such  as  carbon,  hydrogen,  and  oxygen,  but  these  are  taken 
from  the  air  and  from  water.  The  10  necessary  elements 
are:  nitrogen,  potassium,  phosphorus,  magnesium,  sul- 
phur, sodium,  chlorine,  iron,  silicon,  and  calcium.  Not 
one  of  these  is  present  in  soil  as  an  element,  but  each  forms 
a  part  of  some  compound.  Thus,  the  potassium  is  a  part 
of  clay;  the  silicon  a  part  of  clay  and  of  sand;  the  nitrogen 
a  part  of  the  proteids  of  the  humus ;  the  phosphorus  a  part 
of  calcium  phosphate. 

While  10  soil  elements  are  needed  for  plants,  only  3  or  4  are  used  up 
rapidly.  These  are  nitrogen,  phosphorus,  potassium,  and  sometimes 
calcium.  It  is  often  supposed  that  if  any  compounds  of  these  neces- 
sary elements  are  present,  the  soil  is  fertile.  This  is  a  mistake.  The 
elements  must  be  in  such  compounds  that  the  plant  can  absorb  and 
use  them.  One  of  the  necessary  conditions  is  that  they  must  be  in 
compounds  that  are  somewhat  soluble;  for  it  is  the  soil  solution  (cf. 
§  295)  that  actually  reaches  the  absorbing  organs  of  the  plant.  How- 
ever, these  compounds  must  not  be  too  soluble,  or  fertility  will  disap- 
pear, because  the  rain  will  carry  the  compounds  away. 

In  speaking  of  crops  we  must  not  forget  the  forest;  for  trees  are  a 
crop,  as  well  as  rice  or  wheat. 

299.  Loss  of  Fertility. —  When  we  realize  that  plants 
must  be  able  to  find  certain  elements  in  the  soil,  we  can 
see  that  the  loss  of  these  elements  means  the  loss  of 
fertility. 

Fertility  is  lost,  in  the  first  place,  by  the  growing  of 
crops;  for  crops  are  grown  in  order  that  they  may  take  up 
the  constituents  of  the  soil,  and  work  them  up  into  food 
for  man  and  animals.  This  loss  of  fertility  cannot  be 
avoided.  But  there  are  many  other  causes  of  loss  that 


276  ROCKS  AND  SOIL 

can  be  guarded  against.  One  of  them  is  the  too  rapid 
removal  of  soluble  compounds,  by  drainage.  This  is 
often  due  to  improper  cultivation  of  sloping  ground. 
Nitrogen  compounds,  especially,  disappear  in  this  way; 
for  they  are  easily  converted  into  nitrates  of  metals  (cf. 
§  220),  which  are  very  soluble. 

Nitrogen  leaves  a  soil  not  only  because  its  compounds  are  dissolved, 
but  because  they  are  decomposed,  so  that  the  nitrogen  escapes  back  into 
the  atmosphere  (cf.  §  55).  It  was  found,  in  Minnesota,  that  a  long- 
continued  cultivation  of  wheat  upon  a  piece  of  land  caused  6  times  as 
much  nitrogen  to  leave  the  soil  as  was  removed  by  the  crops  harvested. 

If  certain  crops  are  grown  too  long  upon  a  piece  of  land,  its  soil 
becomes  acid,  or  "sour."  This  is  one  of  the  common  causes  of  loss  of 
fertility  (cf.  §  302).  Attempts  to  grow  clover,  alfalfa,  etc.,  upon  acid 
soil  are  almost  sure  to  fail. 

300.  Preserving  and  Restoring  Fertility. —  While  we 
cannot  help  removing  fertility  when  we  remove  a  crop, 
yet  the  loss  is  often  much  greater  than  it  should  be. 
Farmers  are  learning  that,  as  far  as  is  possible,  they  must 
put  back  upon  the  land  everything  not  actually  sold  from 
it.  Hence  they  need  to  preserve  carefully,  and  to  use, 
manure,  the  most  common  of  farm  fertilizers,  so  as  to 
restore  humus  to  the  soil. 

Another  great  aid  in  the  preserving  of  fertility  is  good 
management.  A  farm  cannot  pay  a  profit  if  it  sells  the 
fertility  of  its  soil  at  a  low  price.  The  crops  that  are  sold 
should  be  those  that  take  the  least  possible  fertility  from 
the  farm.  The  crops  that  take  much  fertility,  and  them- 
selves bring  a  low  price,  should  not  be  sold  from  the  farm, 
but  should  be  converted  into  products  that  have  a  greater 
market  value.  Thus,  when  grains  are  cheap,  they  should 


ROTATION  OF  CROPS  277 

be  used  as  cattle  food,  because  the  price  received  for  farm 
fertility  as  meat  is  usually  greater  than  the  price  received 
for  it  as  grain.  Besides,  when  cattle  are  raised,  much  of 
the  farm's  fertility  can  be  restored,  as  manure. 

Dairying  is  profitable,  both  because  dairy  products  bring  a  high 
price,  and  also  because  they  do  not  remove  much  fertility.  If  we  sell 
butter,  for  example,  we  are  selling  chiefly  fat,  composed  of  carbon, 
hydrogen,  and  oxygen  (cf.  §  224) ;  that  is  to  say,  we  are  selling  a  product 
made  out  of  water  and  the  carbon  dioxide  of  the  air  (cf.  §  310). 

301.  Rotation  of  Crops.—  We  can  preserve  the  fertility 
of  a  field  by  plowing  it,  and  then  letting  it  lie  unused,  or 
' '  fallow,"  for  a  year  or  two.  But  this  is  expensive,  for  the 
field  is  bringing  in  no  return.  A  better  method  is  to 
rotate,  or  change,  its  crops.  In  this  way  the  same 
elements  of  the  soil  are  not  removed  year  after  year. 
Sometimes  rotation  consists  in  sowing  buckwheat,  clover, 
etc.,  and  then,  when  they  have  grown,  in  "plowing  them 
under"  (cf.  §  56).  This  treatment  restores  nitrogen  to 
the  soil.  Crops  so  used  are  called  green  manures. 

The  rotation  of  crops  depends  on  the  fact  that  different 
crops  remove  different  materials  from  the  soil.  Grains, 
such  as  wheat,  take  up  much  phosphorus;  grass  takes  up 
little  phosphorus.  Corn  is  exhausting  to  the  soil,  for  it 
removes  much  of  all  three  of  the  elements  nitrogen, 
phosphorus,  and  potassium.  If  the  crop  is  changed  at 
intervals,  the  field  that  has  lost  a  great  deal  of  an  element 
has  time  to  recover,  and  to  get  enough  of  that  element  into 
a  form  in  which  the  plant  can  use  it. 

Rotation  has  other  good  results.  The  root  systems  of  plants  are 
different  (cf.  §  316) ;  hence  one  plant  often  breaks  up  the  ground  for 
another.  A  long  growing  of  the  same  plant  in  a  field  frequently 


278  ROCKS  AND  SOIL 

allows  plant  diseases  or  harmful  insects  to  get  a  strong  foothold. 
When  the  crop  is  changed,  the  new  plant  is  usually  immune;  that  is, 
not  affected  by  the  disease.  Certain  weeds  act  in  a  similar  way. 
They  grow  readily  in  fields  containing  some  one  crop,  and  not  so  easily 
along  with  other  crops.  It  has  also  been  found  that  many  plants 
leave  in  the  soil  substances  called  toxins,  which  act  as  poisons  for  the 
same  kind  of  plant  in  following  years. 

302.  Artificial  Fertilizers. —  Artificial,  or  commercial, 
fertilizers  are  used  when  natural  manures  are  not  abun- 
dant enough,  or  not  of  the  right  sort.  As  commonly  used 
they  contain  one,  two,  or  all  three  of  the  elements  nitrogen, 
phosphorus,  and  potassium.  One  having  all  three  ele- 
ments is  called  a  "complete"  fertilizer. 

The  potassium  compounds  needed  by  the  soil  are  ob- 
tained from  wood  ashes  (when  these  are  to  be  had;  cf. 
§  217),  or  from  deposits,  as  at  Stassfurt,  in  Germany. 
Recently  some  lavas,  and  some  deposits  in  the  West,  have 
been  found  that  give  potassium  compounds  useful  for 
fertilizers. 

The  phosphorus  of  fertilizers  is  in  the  form  of  phos- 
phates, salts  of  phosphoric  acid  (cf.  §§  214  and  221). 
Rock  phosphate  and  the  ashes  of  bones  both  contain 
calcium  phosphate.  They  are  sold  in  the  form  of  a  very 
fine  powder. 

Calcium  phosphate  is  very  slightly  soluble,  so  the 
manufacturers  of  fertilizers  often  change  it  to  acid  calcium 
phosphate  by  treating  it  with  sulphuric  acid  (cf.  §  214). 
The  acid  phosphate  is  called  "superphosphate."  In 
purified  form  it  is  used  for  "acid  phosphate"  baking  pow- 
ders (cf.  §  130).  Land  plaster  is  the  crude  material 
obtained  when  rock  phosphate  is  treated  with  sulphuric 


SUMMARY  .  279 

acid.  It  contains  much  calcium  sulphate,  or  gypsum. 
Sometimes  the  name  is  used  for  powdered  gypsum  itself. 
Nitrogen  is  obtained  for  fertilizers  in  a  number  of  forms. 
Some  of  it  comes  as  sodium  nitrate,  or  " Chili  saltpeter," 
from  the  western  coast  of  South  America.  Ammonia  and 
ammonium  compounds  (cf.  §  112)  are  rich  in  nitrogen,  and 
are  used  as  fertilizers.  The  waste  obtained  in  slaughter 
houses,  such  as  scraps  of  meat,  bones,  hair,  etc.,  is  also 
rich  in  nitrogen,  and  is  converted  into  fertilizing  material. 
The  use  of  such  nitrogen  compounds  depends  on  the  fact 
that  oxidizing  bacteria  (cf.  §§58  and  324)  change  a  great 
deal  of  the  nitrogen  into  nitrates  (cf.  §§  220  and  299)  for 
the  use  of  the  food  plants. 

If  a  soil  becomes  acid,  or  "sour,"  it  needs  a  basic  substance  (cf. 
§  220)  to  make  it  "sweet."  Lime  and  limestone  are  used  for  this, 
purpose.  These  substances  also  have  important  effects  on  the  struc- 
ture of  soil  (cf.  §  295).  A  very  sandy  soil  is  not  fertile,  because  its. 
particles  are  too  far  apart,  and  do  not  retain  water.  Lime  and  lime- 
stone help  to  cement  the  separate  grains  together  (cf.  §  285),  forming  a 
less  porous  soil.  While  they  make  a  sandy  soil  less  porous,  lime  and 
limestone  make  a  clayey  soil  more  porous;  they  separate  the  particles 
of  clay,  which  cohere  too  closely,  by  forming  a  "nucleus,"  or  center, 
to  which  the  clay  particles  can  adhere.  The  soil  particles  are  thus 
made  larger,  and  the  soil  more  porous. 

303.  Summary. —  The  earth's  crust  consists  of  mantle  rock  and  bed 
rock.  Exposed  bed  rock  is  an  outcrop.  Soil  is  the  portion  of  the 
mantle  that  is  used  for  growing  crops. 

Common  rocks  are  sandstone,  limestone,  shale,  granite,  and  con- 
glomerate. 

Rocks  are  stratified,  unstratified,  and  metamorphic. 

Stratified  rocks  are  also  called  sedimentary,  or  aqueous,  rocks. 
They  were  formed,  as  deposits,  under  water. 

Unstratified  rocks  are  also  called  igneous  rocks.     They  are  found 


280  ROCKS  AND  SOIL 

under  all  rocks,  and  often  in  the  cracks  of  stratified  rocks  or  as  over- 
flows over  stratified  rocks. 

Metamorphic  rocks  are  altered  stratified  rocks.  . 

Weathering  is  the  decay  of  rock  because  of  the  action  of  the  ' '  weath- 
er." It  is  due  to  both  physical  and  chemical  action. 

Detritus,  or  talus,  is  the  weathered  rock  at  the  base  of  a  cliff. 

Mantle  rock  is  either  residual  soil  or  drift. 

Drift  has  been  brought  by  air,  water,  or  ice.  Alluvial  soil  was  de- 
posited from  water. 

Glacial  drift  was  brought  by  ice.  In  this  country  it  is  found  as  far 
south  as  the  mouth  of  the  Ohio  River. 

Erosion  is  the  general  cutting  down  of  the  land  level.  The  agents 
of  erosion  get  their  energy  from  gravity. 

Soil  consists  of  loam,  humus,  and  small  organisms,  such  as  bacteria. 
It  must  also  contain  water  and  air. 

According  to  their  general  structure,  soils  are  either  light  or  heavy. 

Soil  particles  are  classified  as  gravel,  sand,  silt,  and  clay. 

Water  is  transferred  through  soil  largely  by  capillary  action. 

Tillage  is  working  the  soil  with  implements.  Plowing  consists  in 
turning  the  soil  over.  Cultivating  is  shallow  plowing. 

Irrigation  is  the  artificial  watering  of  land. 

The  fertility  of  a  soil  is  its  power  of  producing  crops. 

At  least  10  chemical  elements  are  taken  out  of  soil  by  plants,  besides 
the  carbon,  hydrogen,  and  oxygen  taken  from  air  and  water. 

The  3  soil  elements  that  are  used  up  most  rapidly  are  nitrogen, 
phosphorus,  and  potassium. 

Fertility  is  lost  by  the  growing  of  crops,  by  improper  drainage,  by 
permitting  a  soil  to  become  sour,  by  growing  one  crop  too  long,  by 
selling  the  fertility  in  the  wrong  form. 

We  can  restore  fertility  by  allowing  land  to  ' '  lie  fallow/7  by  rotating 
crops,  and  by  using  fertilizers. 

304.  Exercises. 

1.  Are  wood  ashes  as  good  as  lime  for  making  an  acid  soil  sweet? 
Explain. 

2.  A  year  or  two  after  a  fire  has  ' '  burned  over  "  land  having  an  acid 
soil  there  is  often  a  wonderful  growth  of  plants;  why? 


EXERCISES  281 

3.  Does  the  freezing  of  the  ground  in  winter  play  any  part  in  pre- 
paring a  "heavy"  soil  for  plant  growth?    Why? 

4.  Find  out  from  some  farmer  or  gardener  what  kind  of  a  soil,  sandy, 
silty,  or  clayey,  is  best  adapted  to  the  growing  of  garden  vegetables;  of 
corn;  of  grains  like  wheat  and  oats;  of  hay. 

5.  Humus  absorbs  water  more  readily  than  clay  does,  and  less 
readily  than  sand.     What  advantage  is  there  in  having  humus  in  a 
soil? 

6.  What  is  the  economy  of  using  the  cream  of  milk  for  butter,  and 
feeding  the  skimmed  milk  to  young  stock,  such  as  calves  and  pigs? 

7.  What  is  the  economy  of  having  birds  on  a  farm? 

8.  Is  there  economy  or  waste  in  burning  up  the  stubble  of  the  farm? 
Give  both  sides. 


CHAPTER  XV 

PLANTS 

305.  Plants  and  the  Soil. —  The  close  connection  be- 
tween plants  and  the  soil  has  already  been  spoken  of 
(cf.  §  298).     Plants  take  out  of  the  soil  and  the  air  about  13 
elements;  out  of  these  elements  the  higher  plants,  build 
up  complicated  and  beautiful  structures,  known  as  roots, 
stems,  leaves,  flowers,  and  seeds.     We  call  these  struc- 
tures the  organs  of  the  plant  (cf.  §  3).     How  is  it  that 
plants  are  able  to  bring  about  this  wonderful  change  of 
the  materials  of  soil  and  air  into  living  plant  material,  or 
plant ' '  tissue?"     For  the  answer,  in  so  far  as  men  know  it, 
we  shall  need  to  go  to  textbooks  of  Botany.     It  is  enough 
to  say  that  plants  are  living  organisms,  and  that  if  we 
put  the  embryo  plant,  that  is,  the  plant  which  is  enclosed 
in  the  seed,  into  fertile  soil,  and  leave  it  exposed  to  the 
sunshine,  the  air,  and  the  rain,  it  will  sprout  and  grow. 
Sooner  or  later  it  will  become  a  full-grown  plant,  like  its 
parent,  and  will  be  able  to  carry  on  all  the  processes  of 
which  its  parent  was  capable. 

306.  Functions  of  Plants. —  When  we  enumerate  the 
organs  of  the  higher  plants,  as  we  did  in  the  preceding 
section,  we  at  once  think  of  some  special  function,  or  duty, 
which  each  performs  for  the  plant.     We  can  classify  all 
these  special  functions  as  parts  of  two  general  functions, 
which  all  plants  must  carry  out;  for  life  depends  upon 

282 


FUNCTIONS  OF  PLANTS  283 

them.  Plants  must  feed,  and  for  this  purpose  they  must 
have  organs  of  nutrition.  Then,  if  the  species,  or  kind, 
of  plant  is  to  survive,  there  must  be  organs  for  the  pro- 
ducing of  new  members  of  the  species;  these  are  the 
organs  of  reproduction.  Animals,  as  well  as  plants,  must 
carry  out  these  two  elementary  processes  successfully,  if 
they  and  their  kind  are  to  continue  on  the  earth.  The 
higher  plants  carry  out  the  process  of  nutrition  in  their 
roots,  stems,  and  leaves,  and  that  of  reproduction  in 
flowers  and  seeds. 

But  the  plant,  well  as  it  may  be  fitted  to  live,  is  of  no 
consequence  by  itself.  It  must  have  proper  surroundings, 
such  as  soil,  sunlight,  air.  The  presence  of  other  plants, 
of  the  same  or  a  different  kind,  and  of  animals,  also 
affects  greatly  the  future  of  the  plant.  We  call  all  these 
surroundings  of  an  organism,  which  help  or  hinder  its 
development,  the  environment  of  the  organism. 

It  requires  only  a  little  observation  to  show  us  that  the  different 
kinds  of  plants  have  become  accustomed  to  certain  environments. 
Some  do  best  in  shady  places,  others  in  sunshine;  some  prefer  sandy 
soil;  some,  clay;  some,  humus.  We  say  that  each  species,  or  variety, 
has  adapted  itself  to,  or  fitted  itself  for,  its  environment. 

All  the  conditions,  or  influences,  of  the  environment  call  out  some 
action  on  the  part  of  the  plant.  We  call  the  environment's  influence 
the  stimulus  (plural,  stimuli;  we  have  the  same  meaning  in  "stimu- 
late"); the  action  of  the  plant  we  call  its  reply,  or  response,  to  the 
stimulus.  Thus,  we  say  that  light  is  a  stimulus  to  our  eyes,  and  sight 
is  the  eyes'  response.  Light  is  a  stimulus  to  the  sunflower,  too;  the 
turning  of  the  sunflower  toward  the  light  is  one  way  in  which  it  re- 
sponds to  light.  The  environment  is  not  always  quite  the  same;  so 
plants  are  successful  or  unsuccessful  according  as  they  have,  or  have 
not,  developed  parts  to  meet  the  conditions  and  changes  in  their  envi- 
ronment. 


284 


PLANTS 


the  earth. 


307.  Germination  of  a  Bean. —  When  we  put  a  seed  into 
the  ground  under  proper  conditions,  it  responds  to  the 
stimuli  it  receives,  by  germinating.  Germinating  means 
all  the  changes  in  the  contents  of  the  seed  until  the  tiny 
plant  in  the  seed  has  become  an  independent  plant,  or 
seedling.  The  bean  gives  us  a  convenient  seed  for  study. 
If  it  is  soaked  in  slightly  warmed  water,  say,  over  night, 
the  shriveled  surface  becomes  distended,  or  filled,  by  the 
water,  which  passes,  by  diffusion,  through  the  "skin" 
(cf.  §  106).  If  the  bean  is  then  placed  in  a  box  of  earth, 
set  in  a  sunny  window,  and  the  earth  is  kept  moist,  growth 
will  begin.  In  a  few  days  a  curved  "stem"  will  push  up 
When  this  straightens  itself,  it  raises  into  the 
air  the  two  halves  of  the  bean;  between 
them  there  is  a  pair  of  tiny  leaves.  At 
the  lower  end  of  the  small  stem  roots  are 
developed.  As  the  bean  seedling  becomes 
older,  it  forms  pair  after  pair  of  true 
leaves,  always  from  a  growing  "tip";  the 
"halves"  of  the  bean  become  thinner,  turn 
green,  and  finally  fall  off.  The  plant  is 
now  independent  (Fig.  232). 

What  are  the  parts  of  the  original 
seed,  and  what  change  do  they  undergo  in 
germinating?  We  can  answer  these  ques- 
tions by  studying  the  soaked  bean  before 
planting.  We  find  that  the  "halves"  are  enclosed  in  a 
tough  ' '  skin" ;  this  is  the  testa.  All  inside  the  testa  is  the 
embryo.  The  "halves"  are  called  cotyledons,  or  seed 
leaves.  They  contain  food  for  the  embryo.  It  is  for 
this  food  that  we  eat  the  bean.  Between  the  cotyledons 


FIG.  232.  A  Bean 
Seedling,  with 
Its  Roots,  Stem, 
Cotyledons,  First 
Pair  of  True 
Leaves,  and  Leaf 
Bud. 


LEAVES  285 

there  is  a  tiny  bud,  called  the  plumule;  this  gives  rise  to 
the  stem  and  true  leaves  of  the  seedling.  The  cotyledons 
are  at  one  end  of  a  minute,  embryo  stem,  called  the 
hypocotyl  (from  hypo,  i '  under, ' '  and  cotyledon) .  That  end 
of  the  hypocotyl  which  does  not  bear  the  plumule  sends 
out  the  roots  of  the  seedling. 

308.  Other  Seeds. —  The  germination  of  other  seeds  is  slightly 
different  from  that  of  the  bean.     In  many  seeds  the  food  of  the  embryo- 
is  not  stored  in  the  cotyledons,  but  in  a  space  surrounding  the  embryo; 
food  so  stored  is  called  the  endosperm.     In  the  pea  the  cotyledons 
remain  within  the  testa,  supplying  the  nutrition  required  by  the 
growing  embryo  and  seedling.     In  the  castor  bean  the  cotyledons  es- 
cape, but  they  differ  from  those  of  the  garden  bean  in  that  they  become 
large  and  green,  and  do  the  work  of  true  leaves. 

A  large  class  of  plants  has  only  one  cotyledon.  These  are  called 
monocotyls,  while  beans,  peas,  etc.,  are  called  dicotyls.  Corn  (maize) 
is  a  monocotyl.  In  corn  the  embryo  is  at  one  side,  just  beneath  the 
testa.  When  the  testa  breaks  open,  the  embryo  sends  its  plumule- 
upward,  and  the  root  end  of  the  hypocotyl  downward.  The  cotyledon 
and  the  endosperm  remain  inside  the  testa. 

309.  Leaves. —  The  expanded  part  of  the  leaf  is  called 
the  blade.     In  some  plants  the  blade  is  attached  directly 
to  the  plant  stem;  in  other  plants  there  is  a  short  stalk, 
called  the  petiole.     Sometimes  the  plant  produces  tiny 
blades,  called  stipules,  at  the  place  where  the  petiole 
joins  the  stem. 

The  blade  is  marked  by  a  network  of  veins.  If  there  is 
a  prominent  central  vein,  this  is  called  the  midrib.  Veins 
are  arranged  in  three  general  ways  (Fig.  233).  The 
first  leaf  (on  the  left  of  the  figure)  is  palm-veined;  the  sec- 
ond, feather-veined;  the  third,  parallel-veined.  A  leaf 


286 


PLANTS 


may  be  broken  up  into  leaflets,  as  in  the  clover;  it  is  then 
called  a  compound  leaf. 

Where  the  heat  of  the  sun  is  not  too  severe,  as  in  temperate  climates, 
leaves  are  arranged  on  the  stem  in  such  a  way  that  they  shall  receive 
as  much  light  as  possible.  Sometimes  leaves  alternate  upon  the  stem; 
sometimes  two  leaves  are  opposite  each  other.  Often  many  leaves 


FIG.  233.     Leaves  of  the  Maple,  Birch,  and  Wild  Lily-of- the- Valley . 

are  opposite  one  another;  they  are  then  said  to  be  whorled.  Often  all 
the  leaves  are  attached  at  almost  the  same  place  on  the  stem,  but  take 
the  form  of  a  rosette,  so  that  all  shall  get  light. 

The  leaf  is  made  up  of  more  or  less  spongy  tissue,  con- 
sisting of  layers  of  cells.  The  cells  contain  living,  cell 
material,  or  protoplasm  (cf.  §  323),  and  a  green  material, 
called  chlorophyll  (cf.  §  110).  The  outside  of  the  leaf  is 
covered  with  a  skin,  or  epidermis.  This  is  usually  color- 
less. In  the  wall  of  the  epidermis  there  are  slits,  which 
can  be  varied  in  size  by  the  plant;  these  are  called  sto- 
mata  (Fig.  234),  meaning  "mouths."  The  stomata  are 
the  "breathing  pores"  of  the  leaf,  and  enable  the  plant 
to  take  in  air,  and  to  give  off  the  gases  it  does  not 
need.  They  also  control  the  rate  of  evaporation  of  water 


THE  WORK  OF  LEAVES 


287 


from  the  leaf.  In  leaves  that  take  a  horizontal  posi- 
tion the  stomata  are  on  the  under  side.  Sometimes 
there  are  as  many  as  100,000  to 
each  square  inch. 


;: Guard  C«H 


Opening 


FIG.    234.      Breathing    Pore 
(Stoma)  of  a  Leaf. 


Oxygen 


310.  The  Work  of  Leaves.—  The 

leaf  has  several  very  important  du- 
ties to  perform.  For  one  thing,  it 
controls  the  rate  at  which  water 
shall  evaporate  from  the  plant  (cf.  § 
309).  Then  it  also  serves  as  the 
"breathing  apparatus"  of  the  plant, 
taking  in  air,  and  giving  off  carbon 
dioxide,  etc.  Its  third  great  duty  is  to  serve  as  the 

"laboratory"  of  the  plant. 
Here  carbon  dioxide  and 
water  are  brought  together, 
and  are  combined  chemically 
in  compounds  that  the  plant 
uses  for  food  and  for  the 
building  of  its  tissue.  These 
compounds  are  sugar,  starch, 
etc. ;  they  belong  to  the  class 
known  as  carbohydrates 
(cf.  §  184). 

There  is  more  oxygen  in 
the  carbon  dioxide  and 
water,  taken  together,  than 
is  needed  to  form  the  carbohydrate;  so  the  excess  of  oxy- 
gen is  given  off  into  the  air  (Fig.  235).  As  a  result,  the 
green  plant  takes  up  carbon  dioxide  from  the  air,  and 


— ——     Carbon   dioxide 


FIG.  235.    The  leaves  act  upon  the  carbon 
dioxide,  and  produce  oxygen. 


288 


PLANTS 


gives  back  oxygen  in  its  place.  In  this  way  the  process 
by  which  the  plant  prepares  carbohydrates  is  also  the 
process  by  which  it  purifies  the  air  for  the  use  of  animals 
(cf.  §  58).  The  making  of  carbohydrates  out  of  carbon 
dioxide  and  water  requires  chlorophyll  and  light  (usually 

sunlight).  The  combina- 
tion generally  takes  place 
in  leaves;  but  other  green 
parts,  such  as  stems,  also 
carry  it  out. 

311.  Modified  Leaves. 
—  Plants  often  have  spe- 
cial ways  of  supporting 
themselves  or  of  getting 
food.  Thus,  plants  with 
slender  stems  have  the 
climbing  habit.  To  carry 
out  new  functions  the 
plant  seems  to  have  new 
organs ;  but  if  we  examine 
the  plant  carefully,  we 
shall  find  that  the  new 
apparatus  is  simply  one 
of  the  original  structures  (stem,  leaves,  etc.),  altered  to  meet 
the  new  need.  Thus,  the  morning-glory  climbs  because  its 
stem  is  sensitivej  and  twines  around  a  support,  such  as  a 
string  or  a  pole,  Other  plants  have  tendrils  for  support. 

The  tendrils  of  the  pea  are  changed  parts  of  its  compound  leaf 
(cf.  §  309).  Sometimes  the  tendrils,  instead  of  twining  about  an  erect, 
straight  object,  twist  themselves  into  the  rough  bark  of  a  tree.  But 


FIG.  236.     A  Spreading  Elm.     Courtesy  of  the 
Field  Museum  of  Natural  History. 


STEMS 


289 


in  the  ivy,  which  depends  on  brick  or  stone  walls  for  support,  the  tendril 
is  still  further  changed  to  a  sucker,  or  disk.  Leaves  are  often  changed 
to  thorns,  as  in  the  barberry. 

But  it  is  in  the  pitcher  plants,  the  sundews,  and  the  "Venus  fly 
traps"  that  we  see  the  greatest  change  in  leaves.  In  these  plants  the 
leaves  are  altered  so  as  to  form  wonderful  vessels,  or  traps,  for  the 
capturing  of  insects.  The  insects  are  digested  by  the  plant.  Here 
the  order  of  nature  is  reversed;  for  the  plant  consumes  the  animal, 
instead  of  being  consumed  by  the  animal. 

312.  Stems.—  In  our  study  of  the  bean  (cf.  §  307)  we 
learned  that  the  plumule  becomes  the  leaves  of  the  young 
seedling.  The  growth  of  the  plumule  also  produces  a 


FIG.  237.     Under  this  "live  oak"  Sidney  Lanier  wrote  "Marshes  of  Glynn."     Note  the 
Spanish  Moss  on  the  tree.     Courtesy  of  the  Field  Museum. 

part  connecting  leaf  and  root;  this  is  the  stem,  or  stalk. 
The  leaves  borne  by  the  stem  ordinarily  appear  only  at 
certain  places,  called  the  joints,  or  nodes.  The  jointed 
structure  of  the  stem  is  readily  seen  in  the  bamboo  fish- 
ing pole.  The  region  of  the  stem  just  above  the  place 


290 


PLANTS 


where  a  leaf  is  attached  is  called  the  axil  of  the  leaf.    Buds 

and  branches  are  usually  formed  only  in  the  axils  of  leaves 

(cf.  §315). 
Stems  are  of  many  different  sorts.     Some  are  strong 

and  stiff,  and  able  to  bear  a  great  deal  of  weight,  as  is  the 

case  in  trees;  some  run 
along  the  ground,  as  in 
the  strawberry  plant ;  and 
some  seek  a  support,  as 
does  the  stem  of  the 
morning-glory. 

Branches  usually  are 
in  such  positions  that  the 
leaves  get  overhead  light. 
Even  when  branches  be- 
gin by  growing  upward, 
they  are  commonly 
pulled  down  by  gravity, 
as  they  grow  larger,  to  a 
more  or  less  horizontal 
position. 


FIG.  238.      A  Hickory  (Hicoria  pecan). 
Museum  of  Natural  History. 


Field 


In  trees  the  main  trunk 
sometimes  grows  straight  up- 
ward, as  in  the  poplar  and  fir 

(cf.  Fig.  251,  §  327),  and  sometimes  is  divided  again  and  again,  as  in 
the  elm  (Fig.  236),  oak  (Fig.  237),  beech,  and  hickory  (Fig.  238).  As 
a  result  of  the  two  kinds  of  branching,  the  general  outline  of  a  tree 
may  be  either  cone-shaped  or  spreading. 

313.  Structure  of  Stems;  Wood.— If  we  cut  across  a 
growing  woody  stem,  such  as  a  lilac  or  a  maple,  we  shall 
be  able  to  make  out  four  distinct  regions  (Fig.  238a). 


•  STRUCTURE  OF  STEMS;  WOOD 


291 


Epidermis 


Heart 
Wood 


Annual 
Ring 


(1)  An  outer  covering  or  skin,  called  the  epidermis,  as 
in  the  leaf. 

(2)  Next   inward,   a  layer  of  soft   tissue,   called   the 
cortex.     This  is  generally  green. 

(3)  A  wood  layer. 

(4)  A  central  portion,   called  the  pith.     When  trees 
are  hollow,   it   is 

usually  the  pith 
and  the  wood 
nearest  to  it  that 
have  decayed. 

From  the  pith 
to  the  cortex 
there  are  rays, 
like  the  spokes  of 
a  wheel.  These 
are  called  pith 
rays,  or  medullary 
rays.  The  pith 
rays  divide  the 
wood  layer  into 
woody  bundles. 

The  arrange- 
ment just  given  is  that  present  in  all  dicotyls  (cf.  §  308)  and 
in  plants  like  pines  and  firs  (gymnosperms;  cf.  §  327).  In 
plants  having  only  one  cotyledon  in  the  seed,  such  as  corn, 
the  woody  bundles  are  not  arranged  around  a  pith,  and 
separated  by  pith  rays,  but  are  scattered  through  the  stem. 

Trees  with  the  four  regions  just  named  can  grow  thicker 
year  by  year;  the  wood  is  usually  added  in  rings,  called 
annual  rings  (cf.  Fig.  238a).  If  only  one  is  produced  in  a 


Sap  Wood 


Medullary  Ray 

FIG.  238a.     Cross  Section  of  a  Woody  Stem. 


292  PLANTS 

year,  then  the  number  of  rings  indicates  the  age  of  the 
tree  (Fig.  239).  Some  of  the  "big  trees"  of  California 
are  estimated  to  be  between  2,500  and  3,000  years  old. 
They  are  often  35  feet  in  diameter  and  over  300  feet  high. 

Sawing  of  Wood. —  Logs  of  "soft"  wood,  such  as  pine,  spruce,  and 
hemlock,  are  often  floated  down  streams  to  the  sawmills.  Fig.  240 
shows  a  log  "boom,"  or  enclosure,  in  which  logs  are  kept  until  they  are 


FIG.  239.     Felling  a  Great  Tree.     Courtesy  of  the  Field  Museum. 

sawed.  The  log  is  hauled  out  of  the  water,  and  into  the  mill,  by  means 
of  a  moving,  "endless"  chain.  Here  it  is  gripped  by  steel  "dogs," 
which  hold  it  firmly  to  the  log  carriage.  The  carriage  is  then  run  up 
to  the  saw.  The  saw  first  cuts  off  the  rounded  sides  of  the  log,  as 
"slabs."  In  ordinary  sawing,  three  sides  are  thus  "squared";  then 
the  squared  log  is  cut  into  boards  by  cuts  made  parallel  to  one  another. 
This  is  slash-sawing. 

Radial,  or  rift,  sawing  is  a  cutting  along  lines  from  the  outside  of 
the  log  toward  the  center.  The  cuts  are  thus  made  through  the  pith 
rays  (Fig.  240a).  In  slash  sawing,  the  central  board  is  the  only  one 


STRUCTURE  OF  STEMS;  WOOD 


293 


cut  in  this  way.  Boards  made  by  sawing  through  the  pith  rays  are 
better  than  slash-sawed  boards,  because  they  warp  less,  and  have  a 
more  even  grain.  Quarter  sawing  is  radial  sawing.  The  log  is  first 


FIG.  240.     A  Log  Boom.     Courtesy  of  the  Field  Museum. 

cut  lengthwise  into  quarters,  and  boards  are  cut  from  the  quarters  as 
nearly  through  the  pith  rays  as  is  possible.  The  pith  rays  are  the 
''silver  flakes"  that  give  to  quarter-sawed  oak  its  beautiful  marking. 


FIG.  240o.     A  Lengthwise  Section  through  the  Pith  Rays,  Showing  the  Ends  of  Quarter- 
Sawed  Boards. 

Knots  in  boards  are  the  remains  of  branches  which  grew  on  the 
trunk  when  the  tree  was  young.  In  old  trees,  these  remains  have 
been  entirely  covered  up  by  the  annual  rings. 


294 


PLANTS 


314.  Sap. — The  water  and  dissolved  food  which  the 
root  takes  from  the  soil  rise  through  the  stem  to  the 
leaves.     This    dilute    solution    is    called    sap.     The    sap 
passes  upward  through  the  cells  that  make  up  the  woody 

layer  of  the  stem.  As  the 
tree  grows  older,  the  sap 
leaves  the  inner  wood, 
which  is  near  the  pith, 
and  passes  upward  only 
through  the  outer  rings, 
near  the  cortex.  The  in- 
ner wood  is  called  heart 
wood ;  the  outer,  sap  wood 
(cf.  Fig.  238a).  For  lum- 
ber, the  heart  wood  is 
greatly  preferred,  because 
it  does  not  warp  as  much, 
or  rot  as  readily,  as  sap 
wood. 

The  sugar  maple  stores 
away  sugar  in  its  woody 
tissue.  In  the  following 
spring  the  water  that  rises  from  the  roots  dissolves  the 
sugar,  producing  maple  sap.  Men  drill  holes  at  intervals 
into  the  sap  wood,  and  insert  spouts,  down  which  the  sap 
drips  into  collecting  buckets  (Fig.  242).  When  the  sap 
is  boiled  down,  it  gives  maple  syrup  and  maple  sugar. 

315.  Buds. —  Buds  are  structures  for  the  building  of 
leaves,  stems,  and  flowers  (Fig.  243).     Leaf  buds  are  a 
stem  and  its  leaves  in  undeveloped  form.     While  in  the 
bud,  the  stein  is  very  short;  so  that  its  nodes  are  close 


FIG.  242.  Collecting  Maple  Sap.  The  buckets 
ought  not  to  be  open,  and  there  are  too 
many  on  the  tree.  Courtesy  of  U.  S.  Dept. 
of  Agriculture. 


ROOTS 


295 


together.  On  this  account,  the  leaves,  which  on  the 
grown  stem  are  far  apart,  overlap  one  another  in  the  bud, 
and  form  a  compact  bundle.  This  pro- 
tects the  tip  of  the  branch  until  it  is 
ready  to  grow.  The  most  common  buds 
are  dry  and  shiny  on  the  outside,  and 
are  planned  to  keep  out  moisture.  In 
winter  buds  the  inside  of  the  leafy  covers 
is  often  wooly,  in  order  to  protect  the 
young  leaves  and  stem  from  sudden 
changes  of  weather  (cf.  §  75). 


Ovules 


FIG.  243.    Cross  Section 
of  a  Rose  Bud. 


The  "growing  tip"  of  each  stem  and  branch  has  a  terminal,  or 
*'  end,"  bud.  Buds  that  arise  in  the  axils  of  leaves  (cf.  §  312)  are  called 
axillary  buds.  Buds  that  occur  in  unusual  places,  that  is,  not  at  the 
tips  of  branches  or  in  the  axils  of  leaves,  are  called  "unusual,"  or 
adventitious,  buds.  The  young  shoots  that  are  sent  up  by  the  stump 
or  the  root  of  a  tree  are  from  adventitious  buds. 


316. 

carried 


Roots. —  The  work  of  the  leaves  and  the  stem  is 
out  in  the  air  and  the  light;  hence  these  parts 
develop  upward  when  the  seed  ger- 
minates. But  the  duty  of  the  root  is 
to  hold  the  plant  in  a  fixed  place,  and  to 
secure  water  and  food  for  it  from  the 
soil.  Therefore  roots  ordinarily  avoid 
the  light  just  as  strongly  as  leaves  and 
stems  seek  it.  Some  roots,  however, 
such  as  those  of  water  plants,  carry  on 
their  functions  outside  of  the  soil. 


PIG.  241.    Kinds  of  Roots. 


The  root  that  comes  from  the  hypocotyl,  and  all  that  develops  from 
this  root,  is  called  the  primary  root.  Sometimes  the  primary  root  goes 
down  in  one  main  portion,  called  a  tap  root  (Fig.  241).  The  dandelion 


296  PLANTS 

and  the  turnip  have  tap  roots.  Often  the  roots  are  divided  into  many 
branches,  as  in  grass  and  corn.  The  roots  that  come  from  creeping 
stems,  such- as  those  formed  at  the  nodes  of  the  strawberry  plant,  are 
secondary  roots. 

The  root  has  a  growing  tip,  protected  by  layers  of  cells.  Near  the 
tip  the  root  develops  root  hairs.  These  have  delicate  walls,  and  bring 
the  root  into  very  close  connection  with  the  soil  particles,  so  that  it  can 
absorb  water  and  nutriment  (cf.  §  298) . 

317.  Underground  Storage  of  Food. —  We  have  seen 
(cf.  §  307)  that  many  plants  store  away  food  for  the  next 
generation  in  the  cotyledons  or  the  endosperm  of  the 
embryo.  Plants  may  be  annuals,  that  is,  may  die  down 
to  the  ground  each  autumn,  or  they  may  be  perennials, 
which  last  from  year  to  year.  Many  annuals  store  away 
food,  not  in  seeds,  but  in  other  plant  structures.  The 
plant  draws  upon  this  supply  in  the  following  spring,  when 
rapid  growth  begins.  Man  has  developed  some  of  these 
plants,  so  that  they  store  away  food  for  him.  Often 
the  plant  has  an  underground  stem  on  which  under- 
ground leaves  are  developed  for  the  purpose  of  stor- 
age. The  inner  leaves  become  much  thickened,  and 
the  outer  leaves  take  the  form  of  tough,  dry  scales 
that  cover  the  inner  leaves.  Thus  we  get  bulbs.  The 
onion  and  the  lily  are  bulb-forming  plants.  An  under- 
ground stem  is  called  a  rootstock.  The  common  ferns, 
the  wild  ginger,  the  iris,  and  the  bloodroot  have  root- 
stocks. 

When  the  underground  stem  becomes  much  enlarged, 
it  produces  tubers,  such  as  the  potato.  The  surface  of 
the  potato  has  little  scales,  which  are  imperfect  leaves. 
In  the  axils  of  these  scales  (cf.  §  312)  are  the  "eyes" 


FLOWERS  297 

of  the  potato.  The  eyes  are  buds  which,  when  placed  in 
soil,  produce  new  potato  plants. 

Not  only  the  leaf  and  the  stem,  but  also  the  root,  may 
become  thickened,  and  be  used  for  the  storing  of  food. 
The  radish,  turnip,  parsnip,  and  carrot  are  thickened 
tap  roots;  the  sweet  potato  is  a  " fleshy"  branching  root. 

318.  Flowers — We  are  now  to  study  the  flower,  the 
wonderful  organ  through  which  the  higher  plants  repro- 
duce themselves  from  generation  to  generation. 

The  complete  flower  has  four  sets  of  parts  (Fig.  244), 
and  each  of  these  is  usually  arranged  in  a  whorl  (cf.  §  309) 
around  the  flower  stalk.  The  Carpe,s 

outer  set  is  called  the  calyx,  or 
"cup,"  of  the  flower;  its  sepa- 
rate parts  are  called  sepals.  The 
next  set  of  parts  is  called  the 
corolla ;  each  part  of  the  corolla 
is  a  petal.  The  third  set  con- 
sists of  the  stamens,  the  organs 

0  FIG.  244.     Parts  of  a  Flower. 

that  produce  the  pollen.     The 

innermost  set  is  the  carpels;  these  produce  the  seeds. 
The  top  of  the  flower  stalk,  on  which  the  parts  of  the 
flower  are  arranged,  is  called  the  receptacle. 

The  corolla  is  usually  the  attractive,  colored  part  of  the  flower.  The 
calyx  is  often  highly  colored  also,  but  commonly  it  is  green,  like  true 
leaves.  The  flower  is  really  composed  of  modified  leaves  (cf.  §  311). 
The  calyx  and  corolla  are  the  most  leaf-like  parts,  and  enclose  the 
stamens  and  carpels,  the  real  organs  of  reproduction.  Often  the  calyx 
or  the  corolla  is  in  one  piece,  as  a  result  of  the  joining  together  of  the 
sepals  or  the  petals.  We  see  this  in  the  morning-glory  and  the  bluebell. 


298  PLANTS 

The  stamen  consists  of  two  distinct  parts :  the  stalk,  or  filament, 
and  the  pollen  case,  or  anther.  In  flowers  that  have  the  corolla  in  one 
piece  the  stamens  are  often  attached  to  the  corolla. 

The  carpel  of  an  ordinary  flower  consists,  first,  of  a  bulb-like  seed 
case,  or  ovary,  in  which  tiny  ovules,  or  "  little  eggs,"  are  produced. 
Above  the  ovary  is  a  solid  stem,  called  the  style,  which  looks  like  the 
neck  of  a  flask.  The  tip  of  the  style  bears  a  sticky,  outspread  surface, 
called  the  stigma.  In  many  plants  two  or  more  of  the  carpels  are 
united,  so  that  all  the  ovules  are  in  one  ovary.  We  call  the  whole 
group  of  carpels  the  pistil.  Thus,  a  simple  pistil  has  only  one  carpel;  a 
compound  pistil  consists  of  two  or  more  carpels. 

The  number  of  parts  in  flowers  is  important.  Thus,  there  are  usu- 
ally 3  or  5  sepals,  petals,  stamens,  and  carpels.  Often,  however,  the 
number  of  stamens  is  twice  that  of  the  sepals.  The  number  of  petals 
is  also  frequently  doubled.  The  buttercup  has  5  sepals,  5  petals,  and 
often  over  30  stamens.  In  many  flowers  petals,  or  sepals,  or  both,  are 
entirely  wanting. 

319.  Formation  of  Seeds. —  The  structure  of  a  seed 
has  been  given  in  §§  307  and  308;  let  us  now  learn  how 
seeds  are  formed.  Before  the  ovule  in  the  carpel  can 
become  a  seed,  it  must  be  fertilized -by  the  pollen.  When 
the  flower  is  mature,  the  pollen  case  splits,  or  breaks 
open,  and  the  pollen  grains  are  carried  by  the  wind  or 
by  insects  to  the  sticky  surface  of  the  stigma.  Here  the 
pollen  grain  sends  out  a  long  tube  that  carries  the  fertilizing 
pollen  cells.  The  tube  passes  through  the  style  into  the 
ovary,  and  then  into  the  ovule.  When  the  pollen  tube 
reaches  the  ovum,  or ' l  egg,"  within  the  ovule,  the  pollen  cell 
and  ovum  unite.  The  addition  of  the  pollen  cell  to  the 
ovum  causes  the  ovum  to  develop  very  rapidly,  and  it  be- 
comes the  embryo  (cf.  §  307).  The  ovule  forms  a  hard  coat 
(testa)  about  the  embryo,  and  any  vacant  space  is  stuffed 
with  food.  The  completely  prepared  ovule  is  then  a  seed. 


THE  DISPERSAL  OF  SEEDS  299 

The  pollen  used  to  fertilize  a  flower  may  come  from  the  stamens  of 
the  same  flower,  or  from  other  flowers  near  or  far  away.  The  air  is 
often  full  of  pollen  grains.  Many  plants  do  not  depend  on  chance  for 
fertilization,  but  develop  structures  that  attract  insects  or  birds. 
These  creatures  then  carry  the  pollen  from  flower  to  flower.  Thus  it 
comes  about  that  many  flowers  have  a  bright  color  and  a  sweet  odor, 
which  tell  the  insect  where  food  is  to  be  found.  For  some  creatures, 
such  as  butterflies,  the  flower  secretes  a  sweet  liquid,  called  nectar. 
Bees  feed  upon  the  pollen  itself.  The  nectar  is  usually  stored  at  a 
place  beyond  the  organs  of  reproduction,  so  that  the  visiting  insect 
must  brush  against  these  organs.  The  insect  thus  becomes  loaded 
with  the  pollen  grains  of  one  flower,  and  brushes  them  against  the 
stigma  of  the  next  flower  it  visits. 

320.  The  Dispersal  of  Seeds. —  The  parent  plant  is 
usually  not  through  with  its  labors  when  it  has  produced 
the  seed;  it  must  still  provide  the  place  for  the  seed's 
growth.  Most  plants  have  worked  out  a 
method  by  which  the  seed  shall  be  carried 
away  to  new  places.  In  some  plants,  as  in 
violets,  the  seed  pod  bursts  open  with  con- 
siderable force,  scattering  the  seed  to  a  dis- 
tance. The  seed  pod  itself  is  often  arranged 
so  that  it  can  be  carried  off  by  the  air.  Ex- 
amples are  the  winged  seeds  of  the  maple 
(Fig.  245),  and  the  tufted  seeds  of  the  dan- 
delion  and  thistle.  Multitudes  of  seeds  are 
carried  about  by  currents  of  water,  even  by  those  of 
the  ocean  itself.  Seeds  like  the  " stickers"  of  the  cockle- 
bur  and  burdock  are  carried  about  by  animals  to  a  new 
place  for  germination. 

Fruits,  which  are  the  ripened  ovaries  or,  sometimes, 
other  parts  of  the  organs  of  reproduction,  are  also  devices 


300  PLANTS 

used  by  plants  for  the  scattering  of  seed.  The  fruit  is 
carried  away,  and  its  fleshy  part  is  consumed,  while  the 
seed  is  scattered.  Man  has,  of  course,  greatly  developed 
many  natural  fleshy  fruits,  just  as  he  has  developed  roots 
and  stems  (cf.  §  317). 

321.     Exercises. 

1.  Name  some  useful  leaves  of  commerce.     Name  some  useful 
kinds  of  sap.     What  is  made  from  each  kind? 

2.  Why  is  it  that  so  many  perennial  plants  lose  their  leaves  each 
autumn?    Name  several  perennials. 

3.  Suggest  a  reason  why  it  is  best  that  the  sap  should  be  less  abun- 
dant in  winter  than  in  summer  (cf.  §  92). 

4.  Can  you  find  a  plumule  in  the  peanut?    What  are  the  cotyledons 
of  the  peanut?    Cornmeal  or  peanuts  kept  in  a  paper  bag  often  make 
the  bag  greasy.     Why? 

5.  Describe  the  veining  of  the  leaves  of  the  geranium,  of  the  rose, 
and  of  grass.     Name  some  plants  having  compound  leaves. 

6.  Name  some  trees  with  tap  roots.     Describe  the  root  of  the  beet. 
From  what  part  of  the  beet  is  sugar  prepared? 

7.  Why  are  logs  for  wood  cut  in  winter  rather  than  in  summer? 
Why  are  soft-wood  logs  kept  under  water  until  they  are  sawed?     Does 
wood  shrink  more  evenly  in  the  log,  or  in  boards?    What  is  kiln-drying 
of  wood?     Why  do  house  doors  and  windows  "stick-"  in  summer, 
although  they  are  loose  in  winter? 

8.  Why  is  it  possible  for  wood  to  'Hake"  stains?    What  besides 
staining  is  done  to  make  a  wood  with  open  structure  more  durable? 
Why  do  men  like  "hard"  woods  for  interior  finish?    What  are  several 
common  "hard"  woods? 

9.  Ask  a  carpenter  why  shingles  are  made  of  cedar.     Ask  him  why 
shingles  should  be  nailed  with  "cut"  nails  rather  than  with  wire  nails. 
Why  do  cedar  stumps  last  so  long  before  they  rot? 

10.  Why  do  forest  flowers,  like  the  hepatica,  spring  beauty,  blood- 
root,  etc.,  bloom  in  the  early  spring?     Why  do  some  plants  produce 
/flowers_before  they  produce  leaves? 

L" 


CLASSES  OF  PLANTS  301 

11.  On  what  part  of  the  strawberry  are  the  seeds?     Is  the  edible 
*' berry"  an  enlarged  ovary?     What  is  it?    Where  are  the  seeds  of  the 
raspberry?    The  currant?    What  has  happened  to  the  ovary  in  the 
case  of  the  apple?     The  cherry  and  peach? 

12.  Of  what  use  are  branches  and  leaves  in  electric  storms  (cf. 
§  148)? 

322.  Classes   of  Plants. —  The  plants  we  have  been 
studying  are  those  highest  in  development  —  the  flower- 
ing plants.     These  are  composed  of  many  parts,  and  carry 
out   their  functions   in   complicated   ways.     There   are 
plants  that  perform  these  same  functions  in  much  simpler 
fashion;  they  may  have  only  a  single  living  unit,  or  cell, 
for  the  carrying  out  of  all  their  functions.     Between  the 
simplest  plants  and  so  high  a  plant  as  the  daisy  there  are 
all   stages,    or   grades,    of   development.     We   therefore 
divide  plants,  for  the  purpose  of  studying  them,  into 
several  groups,  or  classes,  putting  together  all  those  that 
have  certain  parts,  or  perform  certain  functions,  nearly 
alike,  and  then  separating  this  class  as  sharply  as  we  can 
from  the  plants  that  do  things  in  an  essentially  different 
way.     The  divisions  of  plants,  as  we  need  to  consider 
them,  are  algae  (pronounced  aT-je),  fungi   (pronounced 
fun'-jl),  mosses,  ferns,  and  seed  plants. 

323.  Algae. —  The  algae  (singular,  alga;  the  g  is  hard) 
are  chiefly  water  plants,  and  vary  in  size  from  a  single, 
tiny  cell  to  great  masses  many  feet  long.     They  are  green, 
red,  brown,  etc.,  but  all  contain  chlorophyll,  and  are  able 
to  make  their  own  food.     A  common  alga  is  called  pro- 
tococcus;  this  is  found  as  a  green  stain  on  the  north  side 
of  trees  and  fences.     When  the  green  material  is  examined 


302  PLANTS 

with  a  microscope,  it  is  found  to  consist  of  small  cells 
(Fig.  246).  Often  several  cells  adhere  to  one  another. 
The  cell  consists  of  a  wall  and  of  living  substance  within, 
called  protoplasm  (pronounce  this,  pro'-to-plasm).  The 
denser  part  of  the  protoplasm  is  called 
the  nupleus  of  the  cell.  In  the  proto- 
plasm are  the  grains  of  chlorophyll  that 
give  the  groups  of  cells  their  green  ap- 
pearance. 

If  the  protococcus  cells  are  examined 
carefully,   some  will  probably  be  seen 
FIG.  246.   Protococcus,    that  have  dividing  lines  across  them. 

greatly  magnified.  ° 

Each  of  the  two  halves  may  be  divided 
further,  and  the  new  cells  thus  produced  may  separate 
from  one  another.  As  a  result  we  have  a  whole  group 
of  cells.  Each  cell  contains  its  own  protoplasm,  nucleus, 
and  chlorophyll,  and  is  an  independent  plant.  This 
formation  of  new  cells  is  a  method  of  reproduction. 
It  is  called  reproduction  by  cell-division. 

Another  alga  is  called  spirogyra.  This  is  a  "scum"  found  in 
ponds;  its  cells  are  attached  end  to  end,  so  that  they  produce  filaments, 
or  threads.  The  chlorophyll  bodies  are  arranged  in  spirals. 

Spirogyra  carries  out  reproduction  in  a  different  way  from  proto- 
coccus. Two  cells  in  neighboring  filaments  bend  their  cell  walls  toward 
each  other,  until  they  touch.  Then  the  two  walls  between  them  dis- 
appear, and  the  contents  of  one  cell  pass  over  into  the  other  cell.  The 
materials  of  the  two  cells  form  a  body  called  a  spore.  The  spore,  like 
the  embryo,  endures  through  the  winter,  and  then  germinates,  produc- 
ing a  new  plant.  The  spirogyra  is  thus  reproduced  by  a  sexual  method. 

324.  Fungi. —  Fungi  (singular,  fungus)  form  a  large 
group  of  plants  that  have  no  chlorophyll,  and  cannot, 


FUNGI  303 

therefore,  make  their  own  food  (c/.  §  310).  They  live  by 
attaching  themselves  to  living  plants  or  animals;  or  they 
feed  upon  dead  or  decaying  materials.  An  organism  that 
feeds  upon  other  living  organisms  is  called  a  parasite ;  the 
organism  upon  which  a  parasite  feeds  is  called  the  host. 
A  fungus  feeding  upon  decaying  organic  material  is  called 
a  saprophyte. 

A  yeast  plant  is  a  fungus  having  one  cell.  It  is  repro- 
duced by  budding  (cf.  Fig.  103,  §  129).  Many  centuries 
ago  "wild  yeasts"  were  cultivated  by  man,  and  the  result 
is  our  ordinary  bread  yeast,  or  leaven.  While  feeding 
upon  the  sugar  of  the  dough,  the  yeast  plant  produces 
carbon  dioxide.  This  causes  the  dough  to  rise,  and 
makes  bread  porous  and  light. 

Bacteria,  also  called  microbes,  or  germs,  are  very  small, 
one-celled  fungi  found  everywhere  in  air,  water,  and  soil 
(Fig.  247),  and  in  the  bodies  of  ^  , 

plants  and  animals.  They  are  re- 
produced by  cell-division,  like  pro- 
tococcus.  The  cell  walls  of  bacteria 
usually  have  projections,  called 
cilia,  by  means  of  which  the  cells 
swim  about.  It  is  bacteria  that 
make  milk  and  fruit  juices  "sour/7 
and  cause  meat  to  decay.  These 
changes  are  fermentations,  like  the 
fermentations  due  to  yeast. 

Most  of  the  bacteria  that  live  about  us  are  harmless,  but  others 
cause  diseases  like  typhoid  fever,  diphtheria,  cholera,  and  consump- 
tion, and  must  be  looked  upon  as  our  worst  enemies.  Bacteria  that 
are  of  great  importance  to  us  are  those  that  grow  upon  the  roots  of 


304 


PLANTS 


plants  like  clover,  peas,  and  alfalfa  (cf.  §  56),  for  they  take  nitrogen 

from  the  air,  and  convert  it  into  food  for  plants. 

Moulds  are  fungi  that  grow  upon  fruits,  bread,  shoes,  etc.     We  can 

grow  the  bread  mould  readily  by  covering  damp  bread  with  a  dish 

(Fig.  248). 

Mildews  and  rusts  are  fungi  that 
attack  seed  plants,  and  cause  great 
loss  in  fruit  trees  and  grains.  Mush- 
rooms, toad  stools,  and  puff  balls  are 
also  fungi.  Lichens  (cf.  215)  are  a 
class  of  fungi  that  form  spreading 
masses,  red,  blue,  yellow,  etc.,  in 
color,  upon  trees,  rocks,  and  boards. 


FIG.  248.     Broad  Mould  (Mucor)  wit! 
a  Fruiting  Body  that  produces  Spores. 


325.  Mosses. —  Mosses    are    much    more    highly    de- 
veloped plants  than  fungi  and  algae;  for  they  have  leafy 
stems,  and  organs  similar  to  roots,  which  hold  the  plant 
up  from  the  ground.     In  the  common  form  of 

the  moss,  little,  erect  stalks  are  formed  (Fig. 
249)  for  the  organs  of  reproduction.  The  moss 
does  not  produce  flowers. 

Mosses  send  out  many  leafy  branches,  and 
so  cover  even  bare  rocks  and  mountain  sides 
with  verdure.  They  can  endure  very  dry  and 
very  cold  weather,  renewing  their  growth  as 
soon  as  conditions  are  favorable.  In  cold 
climates  the  moss  of  bogs  and  swamps  is 
changed  to  peat  (cf.  §  118).  This  is  mud 
containing  so  much  carbon  that  it  can  be  used  for  fuel. 

326.  Ferns. —  Ferns  are  plants  of  still  higher  develop- 
ment than  mosses.     Their  peculiar  and  beautiful  leaves 
spring  from  underground  rootstocks  (cf.   §  317).     Each 


SEED  PLAXTS 


305 


"stem"  is  really  a  leaf  stalk.  The  young  leaf  appears 
to  be  rolled  up  in  a  spiral,  and  uncurls  as  it  develops. 
The  leaf  is  a  compound  one  (cf.  §  309), 
with  delicate  and  exquisite  veining. 

The  reproductive  organs  of  the  ferns  we 
ordinarily  see  are  the  grain-like  spots  (sori) 
on  the  back  of  the  leaf  (Fig.  250).  In 
some  ferns,  as  in  the  bracken  fern,  the 
edge  of  the  leaf  is  rolled  in  to  protect 
these  organs. 

The  leaf  "stems"  of  ferns  have  woody 
bundles  (cf.  §  313) ;  hence  the  leaves  are  sup- 
ported easily,  even  when  they  grow  large 
and  tall.  In  the  tropics  there  are  true  ferns  40  feet  high. 


FIG.  250.  Fern  Frond 
(Leaf)  with  Sori 
(Fruiting  Bodies). 


327.  Seed  Plants. —  Only  the  seed  plants  produce 
true  seeds.  The  oldest  seed  plants,  as  the  rocks  of  the 
earth  tell  us,  were  relatives  of  the  pine,  spruce,  and  fir, 

trees  which  we 
call  evergreens 
(Fig.  251).  In  the 
evergreens,  the 
seed  is  produced 
on  the  carpel,  but 
not  in  it.  Hence 
these  plants  are 
called  gymnos- 
perms  (qf.  §  313), 
that  is,  "plants 
with  the  seeds 

FIG.  251.     Evergreens.     In  the  center  a  Norway  pine.    The 
"Christmas  trees"  are  spruce  and  balsam  fir. 


306  PLANTS 

carpels  of  gymnosperms  grow  in  groups,  called  cones. 
These  open  when  the  seed  is  ripe,  and  allow  it  to 
escape.  Gymnosperms  are  also  called  conifers,  that  is, 
"cone  bearers."  The  cones  that  produce  the  seeds  are 
"pistillate"  cones.  Fertilization  is  carried  out  by  pollen 
produced  in  other  cones  called  "staminate"  cones. 

The  leaves  of  the  common  gymnosperms  are  not  shed  at  the  coming 
of  winter.  After  the  new  leaves  have  made  their  growth,  the  old  ones 
fall;  but  the  tree  is  never  without  leaves.  The  leaves  are  usually 
needle-shaped.  In  some  cases,  as  in  the  ' '  Norway  "  pine,  there  are  two 
leaves  in  a  whorl;  in  the  "  white"  pine  there  are  five. 

The  wood  of  the  evergreens  is  "soft"  wood.  It  is  valued  because 
it  is  durable,  even  in  the  "weather,"  and  because  it  is  easily  worked. 
The  wood  of  the  white  pine  is  especially  prized. 

The  most  common  seed  plants,  those  we  have  studied 
in  §§  307  to  320,  do  not  have  the  seed  "naked,"  but  "in 
a  closed  vessel."  For  this  reason  they  are  called  angio- 
sperms  (pronounced  an'-ji-o-sperms).  The  "closed  ves- 
sel" is  the  carpel.  The  most  highly  developed  of  the 
angiosperms,  such  as  the  dandelion,  daisy,  aster,  and 
sunflower,  have  composite  flowers.  In  these  plants  a 
large  number  of  individual  flowers  have  "clubbed  to- 
gether," and  grow  upon  a  single  stalk.  The  center  of 
the  composite  "flower"  is  called  the  disk.  It  contains 
the  disk-flowers  —  a  multitude  of  them  —  each  with  a 
closed  corolla  and  a  full  set  of  reproductive  organs. 
Sometimes  there  are  sepals,  too.  The  next  outer  struc- 
ture, which  looks  like  a  whorl  of  petals,  is  really  a  circle 
of  flowers  —  ray-flowers  —  with  the  corollas  split  open, 
so  that  each  looks  like  a  strap.  Outside  of  all  are  scales, 
which  look  like  sepals. 


DISTRIBUTION  OF  PLANTS  307 

328.  Economic    Plants. —  The    economic    plants,    or 
plants  useful  to  man,  are  very  numerous  and  very  im- 
portant.    Some  have  already  been  named.     Out  of  trees 
man  gets  lumber,  and  by  grinding  up  certain  woods  he 
gets  the  pulp  for  paper.     Certain  grasses,  developed  long 
before  the  dawn  of  history,   became  wheat,   oats,  rye, 
barley,  etc.    Indian  corn  was  native  to  America,  and  was 
developed  by  its  primitive  inhabitants.     The  potato  is  a 
native  of  South  America,  but  was  developed,  so  that  it 
became  edible,  in  Europe.     The  flax  plant  has  given  man 
linen  since  the  distant  past.     Cotton  was  known  in  ancient 
Egypt,  but  its  use  on  a  large  scale  was  impossible  until  the 
invention  of  the  cotton  gin,  which  made  cotton-raising 
profitable  in  America. 

Two  of  the  great  problems  of  agriculture  in  America 
to-day  are:  (1)  how  the  soil  may  be  improved,  so  that  it 
shall  give  the  greatest  possible  yields,  and  yet  retain  its 
fertility;  and  (2)  how  our  grain  plants  may  be  improved, 
so  that  they  shall  bear  most  abundantly,  shall  be  free  from 
pests  and  diseases,  and  shall  be  adapted  to  our  varied 
climate.  To  these  problems  we  may  add  the  problem  of 
the  forests  —  how  they  may  be  used  without  being 
destroyed,  and  the  problem  of  the  fruit  supply,  a  supply 
that  is  making  constantly  increasing  demands  upon 
gardeners,  both  here  and  in  the  tropics. 

329.  Distribution  of  Plants. —  Plants  have  distributed 
themselves  all  over  the  earth;  but  there  are  certain  great 
factors,  or  conditions,  that  fix  the  regions  where  any 
particular  kind  of  plant  can  grow.     The  different  kinds  of 
soil,  and  the  amount  of  rainfall  are  two  of  these  conditions 


308 


PLANTS 


(cf.  §§  272  and  298);  but  the  temperature  is  also  very 
important.  As  the  earth  is  divided  into  temperature 
belts,  or  zones,  plants  are  also  found  distributed  in  belts, 
or  zones.  The  limits  of  temperature,  below  or  above 


FIG.  252.     Cacti:    the  Cereus,  Arizona.      Negative  by  Geo.  D.  Fuller. 

which  plants  find  it  hard  to  continue  their  existence,  are 
about  32°  F.  to  122°  F.,  or  0°  C.  to  50°  C. 

In  the  polar  regions,  lichens,  mosses,  and  willows  can 
just  support  themselves.  In  the  colder  part  of  the 
temperate  zone  there  are  conifers,  such  as  spruce,  fir, 
hemlock;  in  the  warmer  part  of  the  temperate  zone 
deciduous  (leaf  shedding)  trees  are  more  abundant. 
Examples  of  these  are  the  beech,  maple,  birch,  oak, 
hickory,  and  chestnut.  In  the  tropical  zone,  the  palm, 


SUMMARY  309 

cypress,  mangrove,  magnolia,  mahogany,  and  live  oak 
abound,  and  the  forests  are  dense  with  climbing  plants 
and  air  plants. 

Some  of  the  most  interesting  ways  in  which  plants 
adapt  themselves  to  their  surroundings  are  seen  in  dry 
climates  like  our  western  deserts.  The  greatest  problem 
of  plants  under  these  conditions  is  how  to  get  the  most 
water,  and  how  to  lose  the  least.  As  a  result  they  have 
large  and  widely  spreading  roots,  a  thick  skin,  and  a 
small  surface  of  leaves.  The  cactus  (Fig.  252)  is  an 
example  of  such  plants.  Its  leaves  are  modified  to  spines, 
because  it  does  not  need  ordinary  leaves;  and  the  plant 
body  is  a  compact  mass,  so  that  there  is  little  evaporation. 

330.  Summary. —  The  organs  of  a  plant  are  its  roots,  leaves,  flowers, 
etc.,  each  of  which  has  some  particular  function,  or  duty. 

The  two  general  functions  of  all  living  things  are  nutrition  and  re- 
production. 

The  conditions  and  surroundings  of  an  organism  are  its  environ- 
ment. The  influence  of  the  environment  is  a  stimulus  to  the  organism; 
the  change  or  action  in  the  organism  is  its  response  to  the  stimulus. 

Germination  is  the  change  from  seed  to  seedling. 

The  seed  of  a  bean  consists  of  testa  and  embryo.  The  embryo  con- 
sists of  two  cotyledons,  a  hypocotyl,  and  a  plumule.  Nutriment  stored 
in  an  embryo,  outside  of  the  cotyledons,  is  called  the  endosperm. 

Monocotyls  have  only  one  cotyledon. 

Leaves  consist  of  blade,  petiole,  and  sometimes  stipules.  Veining 
may  be  palm-,  feather-,  and  parallel-vemmg.  A  compound  leaf  has 
several  leaflets.  Leaves  may  be  alternate,  opposite,  or  whorled. 

A  leaf  is  covered  with  epidermis,  through  which  there  are  openings 
called  stomata.  Leaf  tissue  consists  of  cells.  Cells  contain  proto- 
plasm, and,  in  green  leaves,  stems,  etc.,  chlorophyll. 

The  leaf  is  the  laboratory  of  the  plant.  In  it  carbon  dioxide  and 
water  are  built  up  into  carbohydrates,  and  oxygen  is  set  free. 


310  PLANTS 

Leaves  are  modified  to  tendrils,  suckers,  thorns,  spines,  etc. 

Steins  consist  of  nodes,  or  joints.  The  kind  of  branching  deter- 
mines the  shape  of  a  tree.  The  stems  of  dicotyls  consist  of  epidermis, 
cortex,  wood  layer,  and  pith.  Annual  rings  consist  of  the  wood  formed 
in  growing  seasons. 

Sawing  may  be  slash-sawing  or  radial-sawing.  Quarter-sawing  is 
radial-sawing. 

Sap  is  the  water  and  dissolved  food  that  rises  through  the  newer 
wood  (sap  wood). 

Buds  are  stems,  leaves,  and  flowers  in  undeveloped  form;  they  may 
be  terminal,  axillary,  or  adventitious. 

Roots  may  be  tap  roots  or  branching  (fibrous)  roots. 

Food  is  stored  in  underground  roots,  leaves,  and  stems.  Under- 
ground stems  are  rootstocks;  underground  storage  leaves  form  bulbs. 

Flowers  consist  of  calyx,  corolla,  stamens,  and  carpels.  Sepals  are 
the  parts  of  the  calyx;  petals,  of  the  corolla.  Simple  pistils  have  only 
one  carpel;  compound  pistils,  two  or  more. 

The  stamen  consists  of  filament  and  anther. 

The  carpel  consists  of  ovary,  style,  and  stigma. 

Seeds  are  formed  after  the  pollen  has  fertilized  the  ovum.  Seeds 
are  dispersed  by  violent  bursting  of  the  seed  pod,  by  winged  attach- 
ments, by  "stickers,"  and  by  fleshy  fruits. 

The  chief  classes  of  plants  are  algae,  fungi,  mosses,  ferns,  and  seed 
plants. 

Algae  are  one-celled  plants  like  protococcus,  spirogyra,  sea  weeds, 
etc.  Their  reproduction  is  by  cell-division  or  by  sexual  methods. 
Algae  contain  chlorophyll. 

Fungi  are  moulds,  yeast  plants,  bacteria,  mildews,  mushrooms, 
lichens,  etc.  They  contain  no  chlorophyll,  and  feed  upon  living,  dead, 
or  decaying  plants  or  animals. 

Bacteria  produce  fermentations,  as  in  the  souring  of  milk,  decay, 
etc.  Certain  kinds  produce  disease. 

Mosses  have  leafy  stems,  and  root-like  organs,  but  they  do  not 
produce  woody  stems  or  flowers. 

Ferns  produce  woody  bundles  in  their  leaves;  but  their  stems  are 
underground. 


EXERCISES  311 

Seed  plants  produce  true  seeds,  and,  in  trees  and  shrubs,  produce 
woody  stems. 

Classes  of  seed  plants  are  gymnosperms  and  angiosperms. 

Composite  flowers  are  the  highest  form  of  plant  organization. 

Economic  plants  are  of  great  importance  for  man,  in  that  they  give 
him  food,  clothing,  shelter,  and  tools. 

Plants  are  distributed  in  great  zones,  corresponding  to  the  zones  of 
temperature. 

\ 
331.     Exercises. 

1.  What  precautions  are  necessary,  in  the  canning  of  fruit,  to  keep 
it  from  spoiling?    Why?    Why  are  meat,  milk,  compressed  yeast,  etc., 
kept  in  cold  refrigerators? 

2.  How  do  preservatives,  like  formaldehyde,  borax,  etc.,  prevent 
the  decay  of  food?    If  digestion  is  a  series  of  fermentations  (cf.  §  368), 
will  a  food  containing  preservatives  be  easily  digested? 

3.  Why  do  not  fungi  produce  chlorophyll?  When  a  potato  sprouts 
in  a  dark  cellar,  why  are  its  leaves  and  leaf  stalks  white?  How  is 
celery  bleached? 

4.  Is  it  a  good  plan  to  put  away  fresh,  warm  bread  in  a  covered 
box?    Why? 

5.  Do  you  think  it  possible  that  some  of  our  wild  grasses  might  be 
cultivated  so  as  to  become  useful  grains?    How  could  this  be  done? 
What  fruits  have  been  developed  by  the  cultivation  of  inferior  or  wild 
varieties? 

6.  Many  plants  in  the  tropics  have  thick-walled  leaves  with  tips 
in  the  form  of  gutters.     To  what  two  sets  of  conditions  have  they 
adapted  themselves? 

7.  Why  is  it  necessary  for  the  leaves  of  evergreens  growing  in  cold 
climates  to  be  thick  and  needle-shaped  rather  than  thin  and  spreading? 

8.  What  are  some  commercial  uses  of  moss? 

9.  How  does  the  cultivated  rose  differ  from  the  wild  rose?    Ask  a 
gardener  whether  the  cultivated  rose  can  be  reproduced  from  seeds. 


CHAPTER  XVI 

ANIMALS 

332.  What  is  an  Animal? — We  have  already  studied 
something  of  the  relation  between  animals  and  plants. 
Plants  (those  containing  chlorophyll;  cf.  §  310)  change 
carbon  dioxide,  water,  and  the  minerals  of  the  soil  into 
living  material,  which  serves  as  food  for  the  animal  world. 
In  taking  carbon  dioxide  from  the  air,  plants  remove  a 
waste  product  of  animals,  and  restore  oxygen  in  its  place. 
Thus  they  keep  the  composition  of  the  air  the  same,  year 
after  year.     It  was  once  supposed  that  plants  did  not 
produce  carbon  dioxide.     This  is  a  mistake.     Plants  give 
off  carbon  dioxide  in  their  respiration,  just  as  animals 
do;  but  green  plants  take  up  much  more  than  they  give 
off.     Hence  they  seem  not  to  produce  any. 

In  general,  we  may  say  that  an  animal  is  an  organism 
that  cannot  build  up  its  food  out  of  mineral  matter,  while  a 
plant  can.  Plants  having  no  chlorophyll  (fungi)  are  excep- 
tions to  this  statement  (cf.  §  324).  The  lowest  forms  of 
animals  and  plants  are  really  so  much  alike  that  it  is  often 
hard  to  say  to  which  class  a  given  creature  belongs.  The 
fact  that  the  higher  animals  can  move  about  freely  is  not  a 
real  difference;  for  many  animals  are  attached  to  some 
fixed  place,  while  some  plants  have  very  rapid  movements. 

333.  One-Celled  Animals. —  In  stagnant  water  or  in 
mud  there  is  often  found  a  bit  of  jelly-like  substance  that 

312 


ONE-CELLED  ANIMALS  313 

shows,  under  the  microscope,  a  peculiar  power  of  chang- 
ing its  shape,  and  of  moving  about.  This  is  one  of  the 
lowest  animals;  it  is  called  an  ameba  (Fig.  253),  from 
a  Greek  word  meaning  "to  change." 
The  jelly-like  creature  consists  of  a 
cell  of  protoplasm  (cf.  §  323).  At  its 
center  the  cell  is  grainy;  this  region 
is  the  nucleus.  The  ameba  thus  con- 
sists of  one  cell,  like  protococcus;  but 
it  has  no  chlorophyll.  It  has  no  FlG<  2Sagnffinedmeba' 
organs,  either.  It  moves  by  extend- 
ing the  cell  wall  at  any  region  into  a  projecting  lobe; 
the  cell  contents  then  flow  into  the  lobe.  These  lobes 
are  called  "false  feet."  The  ameba  has  no  mouth;  it 
feeds  by  extending  two  lobes  around  an  article  of  food, 
and  then  withdrawing  the  cell  wall.  The  protoplasm 
simply  envelops  the  food.  The  ameba  excretes  (throws 
out)  waste  parts  of  its  food  merely  by  moving  away 
from  them.  When  food  is  thus  passed  through  the  cell 
wall,  no  opening  is  left;  just  as  there  is  no  break  in  the 
tough,  though  fragile,  film  of  a  soap  bubble  when  a  needle 
is  put  through  it. 

The  reproduction  of  the  ameba  is  also  o'f  the  simplest 
sort.  The  nucleus  of  the  cell  divides  itself  into  two  parts, 
half  of  the  protoplasm  groups  itself  about  each  nucleus, 
and  at  the  line  thus  formed  the  cell  divides ;  there  are  now 
two  amebas  instead  of  one. 

A  creature  like  the  ameba  forms  a  part  of  our  own  blood  (cf.  §  378). 
If  you  will  examine  a  drop  of  blood,  under  the  microscope,  you  will 
see  that  it  contains  both  red  and  colorless  bodies.  These  are  called 
corpuscles,  that  is,  ' 'little  bodies."  The  colorless  ones,  called  white 


314 


ANIMALS 


Cilia 


Mouth 


FIG.  254.  Slipper  Animalcule  (Para- 
mecium),  magnified.  View  of  the 
Under  Side. 


FIG.  255.  Bell  Ani- 
malcule (Vorticel- 
la),  magnified. 


corpuscles,  have  the  form  and  the  simple  structure  of  the  ameba;  but 
they  are  not  so  active. 

A  more  highly  developed  one-celled  animal  is  called  the  "  slipper 
animalcule,"   from  its  shape   (Fig.   254).     Animalcule   (pronounced, 

an-i-mal-kul)    means     "  little    ani- 
mal."    The   scientific   name  of   the 
creature    is    paramecium.     In    this 
case   the  cell   has 
a  permanent  place 
for  feeding,  called 
the  mouth,  and  the 
mouth  extends  in- 
ward, forming  a  gullet.     The  creature  has  a  per- 
manent shape,  because  its  cell  wall  is  more  stiff  than 
that  of  the  ameba.     It  swims  about  by  waving  the 
thread-like  extensions  (cilia;  cf.  §  324)  of  its  cell  wall. 
A  third  one-celled  animal  is  called  vorticella,  or 
the  "bell  animalcule"  (Fig.  255).     Its  shape  is  like 
that  of  a  bell  with  a  long  handle.     It  is  called  vor- 
ticella because,  by  waving  the  cilia  at  its  mouth, 
it  produces  a  vortex,  or  whirlpool,  by  which  food 
is  carried  into  the  cell.     The  cell  wall  is  ex- 
tended to  form  a  "  stalk,"  by  which  the  creature 
attaches  itself  to  weeds,  or  to  sticks  and  stones 
in  the  bottom  of  ponds. 
I 

334.  Simple  Many-Celled  Animals; 
Hydra. —  If  a  water  plant  is  placed  in 
a  glass  vessel  of  water,  a  hydra  (Fig. 
256)  is  often  found  attached  to  the 
plant  or  to  the  sides   of  the   vessel. 
It  is  a  brown  or  greenish  creature  half 
an  inch  long,  or  less. 
When  it  is  not  disturbed,  the  hydra  extends  several 
thread-like  "arms/'  called  tentacles,  about  in  the  water. 


Endode.m 

FIG.  256.  Hydra,  or  Polyp. 
Exterior  View  and  Cross 
Section.  Magnified. 


SIMPLE,  MANY-CELLED  ANIMALS;  HYDRA  315 

If  tiny  bits  of  meat  are  dropped  near  them,  the  tentacles 
direct  the  meat  to  the  mouth.  But  food  does  not  go 
directly  into  the  cell,  as  it  does  in  one-celled  animals. 
We  can  see  that  this  is  not  necessary,  for  the  hydra's 
body  and  tentacles  are  made  up  of  two  rows  of  cells. 
The  inner  cells  have  the  duty  of  digesting  food,  while  the 
outer  cells  serve  to  protect  them.  The  digested  food  is 
passed  through  the  cell  walls,  from  the  inner  cells  to  the 
outer  ones.  The  tentacles  do  not  simply  push  food 
toward  the  mouth,  but  some  of  their  outer  cells  have 
stinging  weapons  for  paralyzing  the  hydra's  prey. 

Often  the  hydra  may  be  seen  budding,  as  yeast  does 
(cf.  Fig.  103,  §  129).  The  young  hydra  remains  attached 
to  the  older  one  for  a  time,  and  then  separates  from  it. 
If  a  hydra  is  cut  in  two,  each  half  produces  the  necessary 
cells,  and  forms  a  new  creature.  The  hydra  is  also  re- 
produced by  a  sexual  method.  There  are  not  two  sexes, 
but  some  of  the  cells  produce  egg-like 
bodies,  and  other  cells  on  the  same  hydra 
produce  swimming  cells  that  fertilize  the 
egg-like  cells.  When  the  two  kinds  of 
cells  unite,  they  form  an  embryo  hydra. 
This  falls  to  the  bottom  of  the  water,  and 
in  time  develops  into  a  full  grown  animal. 

More  highly  developed  forms  of  the  hydra 
have  a  great  number  of  animals  in  a  colony  (Fig. 
257) .     The  colony  has  root-like  ' '  holdfasts, ' '  and        FlG- 
attaches  itself  to  rocks.     Hydra-like  animals  are 
called  polyps,  from  words  meaning  "many  feet."    The  coral  polyp 
is  a  common  form.     Each  coral  polyp  takes  limestone  from  sea  water, 
and  forms  a  hard  internal  structure  (coral),  which  remains  when  the 


316 


ANIMALS 


FIG.  258.     A  Sim- 
ple Sponge. 


creature  dies.    The  accumulations  of  coral  rock  —  limestone  taken 
from  sea  water  in  past  ages  —  are  enormous  in  extent  (cf.  §  132). 

Sponges  (Fig.  258)  are  many-celled  animals  less 
well  developed  than  hydras.  The  individual  creature 
has  two  cell  layers  separated  by  a  gelatinous  layer. 
The  gelatinous  layer  produces  the  tough,  horny  mate- 
rial that  we  call  "  sponge."  The  animal  is  very  soft, 
and  the  horny  structure  keeps  its  body  cavity  open. 
The  cells  have  cilia,  which  produce  incoming  water 
currents  bearing  food.  The  outer  openings  of  the 
body  cavities  form  the  tiny  pores  of  the  "  sponge." 
Our  sponges  therefore  represent  colonies  of  the 
sponge  animal  with  the  horny  material  joined  in  a 
large  mass.  Some  sponges  form  skeletons  of  lime- 
stone or  of  silica  (the  substance  of  powdered  quartz),  instead  of  horny 
structures. 

335.  Starfishes. —  One  of  the  interesting  pastimes  at 
the  seashore  is  watching  the  movements  and  other 
activities  of  the  starfishes  (Fig.  259).  The  starfishes 
belong  in  a  class  with  sea-urchins, 
sea-cucumbers,  etc.  This  class  is 
more  highly  developed  than 
sponges  and  hydras. 

The  grown  starfish  is  arranged 
on  a  plan  of  5.  The  central  region 
is  round,  and  the  "points  of  the 
star,"  or  "arms,"  branch  out  from 
it.  The  covering  of  the  animal 
contains  hard  limestone  knobs  with 
projecting  spines.  The  body  has  a  digestive  system  that 
is  distinct  from  the  interior  cavity  (cf.  §  334) ;  it  has  also 
a  simple  nervous  system,  and  the  beginnings  of  a  blood 
system. 


FIG.  259.     Starfish. 


WORMS  317 

On  the  lower  (ventral)  side  of  the  "arms,"  or  "rays," 
the  hard  coverings  are  turned  inward,  forming  five 
grooves.  Extending  out  of  the  grooves  are  many  delicate 
tubes  ending  in  suckers.  These  "  tube  feet "  can  be 
lengthened  and  shortened.  The  animal  attaches  itself 
to  rocks  by  means  of  the  suckers,  and  then  pulls  itself 
along.  It  moves  in  any  direction.  At  the  end  of  each 
ray  there  is  a  tentacle,  which  is  probably  an  organ  for 
smelling,  and  on  each  tentacle  there  is  a  red  spot,  which  is 
sensitive  to  light,  and  is,  therefore,  a  very  simple  eye. 

The  exchange  of  gases  (respiration)  does  not  take  place  in  all  the 
cells  of  the  starfish,  as  in  the  simplest  creatures,  but  in  certain  definite 
spaces.  These  spaces  thus  form  the  beginnings  of  a  breathing  system. 
The  starfish  is  able  to  open  the  shell  of  the  oyster,  and  to  get  at  the  soft 
body  within.  It  then  turns  a  part  of  its  stomach  inside  out  over  the 
oyster,  and  digestion  goes  on  outside  of  the  body.  The  shell  it  simply 
leaves  behind.  If  a  piece  of  a  starfish  is  broken  off,  the  cells  that 
remain  produce  new  cells,  and  replace  what  has  been  lost. 

336.  Worms. —  The  student  must  not  think  of  caterpil- 
lars, grubs,  and  "measuring  worms"  as  worms;  they  are 
the  larva  stage  in  the  development  of  insects  (cf.  §  339). 

Dorsal  Blood  Vessel     Muscles 

^P  Esophagus 

Pharynx 
Brain 


FIG.  260.     The  Earthworm.     Several  segments  are  omitted. 

True  worms  do  not  change  into  anything  else,  but  always 
retain  their  " worm-like"  form.  Worms  include  earth- 
worms (' '  angle  worms  ") ,  leeches,  and  many  marine  worms. 
The  most  common  of  thesf  is  the  earthworm  (Fig.  260). 


318  ANIMALS 

The  earthworm  has  a  long  body,  divided  by  crosswise 
rings.  The  body  has  a  definite  head  (anterior)  end.  If 
we  were  to  divide  the  body  lengthwise,  from  top  to  bot- 
tom, the  two  halves  would  be  similar.  We  say  that  such 
a  body  has  two-sided  (bilateral)  symmetry.  The  earth- 
worm has  a  mouth  at  the  front  of  the  under  (ventral)  side 
of  the  body,  and  a  body  cavity  the  whole  length  of  the 
body.  Waste  material  is  excreted  through  openings  in 
each  side  of  the  body  "rings."  There  is  a  nervous 
system,  with  a  brain  at  the  front  of  the  body.  The 
nerve  cords  are  on  the  ventral  side  of  the  body;  not,  as 
in  higher  animals,  along  the  dorsal  side  (the  back). 

The  earthworm  has  two  sets  of  muscles  in  each  "ring." 
One  set  goes  around  the  body.  When  this  set  contracts, 
the  ring  grows  smaller  in  diameter.  The  other  set  of 
muscles  is  from  front  to  back,  in  each  ring.  When  these 
contract,  the  ring  grows  narrower,  and  the  whole  body 
becomes  shorter.  By  extending  a  portion  of  the  body, 
by  then  holding  on  to  the  ground,  and,  finally,  by  con- 
tracting the  extended  portion,  the  worm  is  able  to  move 
along. 

The  earthworm's  blood  "circulates"  in  two  lengthwise  vessels. 
Contractions  take  place  at  certain  places  called  "  hearts,"  and  form 
waves  that  pass  through  the  vessels.  Respiration,  or  communication 
between  the  blood  and  the  air,  takes  place  through  the  body  wall, 
especially  at  certain  thin  places;  there  are  no  gills  or  lungs.  Worms 
are  reproduced  by  the  sexual  method.  If  a  worm's  head  or  "tail" 
is  cut  off,  as  often  happens  in  the  plowing  or  spading  of  ground, 
each  portion  can  replace  the  rings  it  has  lost,  and  produce  a  perfect 
worm. 

In  digging  its  burrows  the  earthworm  swallows  the  soil,  and  extracts 
whatever  food  the  soil  contains.  Then  it  casts  off  the  soil  in  little 


Kidrjey    Ventricle 
Posterior  Adducto 


Anterior  Adductor 


MOLLUSKS  319 

heaps  (" castings")  at  the  opening  of  the  burrow.  In  this  way  the 
earthworm  makes  the  soil  porous,  and  brings  subsoil  to  the  surface 
(cf.  §  296). 

337.  Mollusks. —  Clams  and  oysters  are  mollusks  that 
live  in  salt  water.  A  very  similar  form,  the  mussel, 
lives  in  fresh-water  lakes  and  in  streams.  "Mollusk" 
comes  from  a  word  meaning  "soft,"  and  is  given  to  this 
class  of  animals  because  of  their  soft  bodies. 

The  mussel  (Fig.  261)  is  found  at  the  water  bottom, 
slowly  plowing  its  way  through  mud  or  sand.  It  has  a  shell 
made  of  two  similar 
parts  (valves) ;  these 
are  joined  at  the  top 
(the  dorsal  side  of 
the  animal)  by  a 
hinge.  Inside  the 
shell  is  the  mantle, 

a     Soft.     mUSCUlar        FlG-  261.     Freshwater  Clam,  or  Mussel;  its  Principal 

Organs. 

structure.    This  lines 

each  of  the  valves.  The  "foot"  of  the  animal  projects 
from  the  anterior  (head)  end  of  the  body.  At  the  oppo- 
site (posterior)  end  there  are  two  openings  called  siphons. 
The  lower  of  these  has  organs  like  cilia,  for  forcing  a 
current  of  water  through  the  body.  The  other  siphon  is 
for  outgoing  water.  The  mussel's  food,  as  well  as  its  air, 
comes  to  it  in  the  water  taken  in  at  the  lower  siphon. 
Between  the  mantle  and  the  foot,  one  on  each  side,  are 
the  gills,  through  which  respiration  takes  place. 

The  halves  of  the  shell  are  held  together  at  the  hinge  by  a  tough, 
horny  ligament.  The  outer  layer  of  the  shell  is  made  of  the  same  horny 
material.  Inside  this  there  is  a  layer  of  limestone,  and  on  the  inner 


320  ANIMALS 

surface  of  the  shell  there  is  "  mother-of-pearl/'  which  consists  of  alter- 
nate, thin  layers  of  limestone  and  horny  material.     The  shell  is  made 
(secreted)  by  the  mantle.    Some  mollusks  form  pearls  (which  are' 
mother-of-pearl  in  round  masses),  if  some  irritating  substance  comes 
between  the  mantle  and  the  shell. 

The  shell  of  the  mussel  springs  apart  when  the  animal  is  dead. 
While  alive,  the  creature  holds  the  halves  together  by  means  of  two 
powerful  muscles  (anterior  and  posterior  " adductors"  of  Fig.  261). 
One  end  of  each  muscle  is  attached  to  the  right  valve,  and  the  other 
end  of  each  to  the  left  valve.  When  the  muscles  contract,  the  valves 
come  together  with  great  force.  The  mussel,  like  the  earthworm,  has 
a  nervous  system,  with  a  brain  at  the  anterior  end  of  the  body,  over 
the  mouth.  .  • 

Mussels,  clams,  and  oysters  are  called  bivalves,  because  of  the  two 
halves  of  their  shells.  Snails  are  called  univalves,  because  the  shell  is 
in  one  piece.  Slugs  are  like  snails,  but  they  form  no  shell.  To  the 
mollusks  belongs,  also,  the  devil  fish,  or  octopus,  the  "  nightmare  of 
the  sea." 

338.  Crustaceans. —  Crustaceans  are  so  called  from 
their  hard  body  covering.  The  class  includes  crayfishes, 
lobsters,  crabs,  barnacles,  etc.  (Fig.  262). 

The  crayfish,  like  the  mussel  and  the  earthworm,  has 
its  parts  arranged  symmetrically.  Like  the  earthworm 
it  has  a  number  of  joints,  or  segments,  each  of  which 
makes  up  a  part  of  the  length  of  the  body.  In  the  cray- 
fish many  of  these  joints  have  very  well  developed  parts, 
or  appendages,  popularly  called  "legs,"  "claws,"  "feel- 
ers," etc.  The  hard  covering  of  the  body  has  already 
been  spoken  of.  This  holds  and  protects  the  soft  organs 
within.  At  the  posterior  end  (abdomen)  the  body  cover- 
ing is  in  several  pieces;  the  remainder  of  the  body,  that 
is,  the  head  and  thorax  (chest),  are  inside  one  piece  of 
covering.  The  so-called  ' '  legs ' '  and  ' '  claws ' '  are  attached 


CRUSTACEANS 


321 


at  the  thorax.  The  eyes  are  attached  to  ' '  stalks  "  on  the 
head.  All  these  appendages  consist  of  joints,  so  that 
they  may  be  bent.  The  segments  of  the  abdomen  have 
smaller  appendages  for  use  in  swimming.  The  jointed 
abdomen  can  itself  be 
bent  very  easily.  Thus 
the  crayfish  is  able  to 
make  a  very  swift 
backward  motion  (to 
' '  crawfish  " )  by  giving 
its  "tail"  a  downward 
and  forward  stroke. 

The  crayfish  has  powerful 
jaws  for  seizing  and  tearing 
food,  and  a  large  stomach 
containing  a  tooth-like  struc- 
ture for  crushing  food. 

The  blood  is  circulated 
by  a  heart,  which  beats  vig- 
orously. The  heart  contains 
only  one  chamber,  and  is  set 
into  a  receiving  space.  This 
space  contains  blood  brought 
from  the  gills.  When  the 
heart  muscles  contract,  they 
make  the  heart  cavity  smaller.  The  compressed  blood  in  the  cavity 
then  opens  the  valve  leading  to  the  arteries,  and  at  the  same  time 
closes  the  valve  from  the  receiving  space  in  which  the  heart  is  sus- 
pended. When  the  heart  muscles  are  relaxed,  the  pressure  of  the 
blood  in  the  arteries  closes  the  valves  opening  out  of  the  heart,  and 
the  pressure  in  the  receiving  vessel  opens  the  valves  leading  into  the 
heart.  Hence  the  heart  is  refilled  with  blood  that  has  passed  through 
the  gills  and  been  purified.  This  blood  it  pumps  to  all  the  organs 
of  the  body.  The  gills  are  placed  below  the  head-thorax  covering, 


FIG.  262.     The  Lobster. 


322 


ANIMALS 


and  the  water  near  them  is  kept  in  constant  motion  by  little  plates, 
or  "  paddles."  The  motion  of  the  water  is  produced  by  appendages 
to  which  the  plates  are  attached. 

As  the  crayfish  increases  in  size,  it  must  have  a  larger  "house;"  so 
it  sheds  its  outer  covering  from  time  to  time,  and  goes  into  hiding 
until  its  new  "shell"  has  grown. 

339.  Insects. —  Insects  and  spiders  have  the  same 
general  structure  as  the  crayfish,  but  they  also  differ  from 
it  in  many  ways.  The  word  insect  means  "cut  into 
parts,"  and  indicates  that  these  creatures  are  made  up 
of  joints.  True  insects  have  a  tough,  horny  covering,  as 
the  crayfish  has,  but  the  head  and  the  thorax  are  separate 
instead  of  united.  The  legs  are  attached  to  the  thorax. 
When  there  are  wings,  as  in  flying  insects,  these  are  also 
attached  to  the  thorax.  Respiration  takes  place  in  tube- 
shaped  air  passages  in  the  different  segments  of  the  body, 
and  not  in  gills.  The  muscles  of  insects  are  very  highly 
developed;  we  see  the  result  in  the  jumping  of  the  grass- 
hopper and  the  flea. 

One  of  the  most  fascinat- 
ing things  about  insects  is 
the  complete  change,  or 
metamorphosis  (pronounced 
met-a-mor'-phos-is),  which 
they  undergo  as  they  de- 
velop. Thus  the  eggs  of  the 

FIG.  263.     Stages  in  the  Development  of        fly   (Fig.  263)  produce  white, 

crawling  creatures  (mag- 
gots). We  call  the  "worm-like"  young  of  insects  larvae 
(singular,  larva).  After  about  a  week  of  rapid  feeding, 
the  larva  of  the  housefly  grows  a  "shell"  about  itself,  in 


INSECTS 


323* 


Egg  Mass 


Larva 


FIG.  264.     The  Mosquito. 


which  it  undergoes  its  change.     In  this  shell,  or  puparium, 

it  is  called  the  pupa  (pronounced  pu'-pa),  or  chrysalis. 

In  about  another 

week  the  creature 

emerges  from  its 

shell  —  a  fly. 
The  egg  of  the 

mosquito  (Fig. 

264)   is  deposited        Pupa 

in    water,    and 

hatches    to    form 

a  "wiggler"   (the 

larva),  which  swims  about  in  the  water.     The  wiggler 

breathes  through  the  end  of  its  "tail,"  and  must  come 

to  the  surface  for  air.    We  can  kill  it  by  putting  a  film 

of  kerosene  on  the  water,  as  the  film  cuts  off  its  air 

supply.  The  wiggler  sheds  its  "skin"  often,  and  thus 
changes  into  the  pupa.  Finally  the 
flying  mosquito  comes  out  of  the 
pupa  "skin." 

Perhaps  the  most  wonderful  of 
insect  changes  are  those  by  which 
the  caterpillar  becomes  a  chrysalis, 
and  the  chrysalis  a  butterfly.  Some 
moths  spin  cocoons ;  true  butterflies 
do  not. 

FIG.  265.    A  Wasp's  Nest. 

The  most  highly  developed  insects  are 

ants,  bees,  and  wasps  (Fig  265).  In  the  case  of  the  bees,  some  eggs 
develop  without  being  fertilized.  These  form  the  male  bee,  or 
drone.  The  fertilized  eggs  produce  female  bees,  but  only  a  few 
of  the  females  —  the  queens  —  become  capable  of  laying  eggs. 


324  ANIMALS 

The  greater  part  of  the  females  remain  undeveloped,  and  are  the 
workers. 

Ants,  like  bees,  have  a  highly  developed  form  of  "society."  Some 
ants  act  as  soldiers,  and  protect  those  that  work.  Certain  ants  cap- 
ture other  ants,  and  make  them  work.  Other  ants,  still,  have  plant 
lice  for  their  "cows,"  and  feed  upon  the  liquids  they  produce. 

Some  of  the  insects,  such  as  the  bees  and  the  larvae  of  the  silk- 
worm, are  useful  to  man;  but  others,  like  the  mosquito  and  fly,  are 
only  a  nuisance  and  a  danger  (cf.  §  424).  But  in  numbers  the  insects 
and  spiders  probably  exceed  all  other  animals  put  together. 

340.  Exercises. 

1.  What  is  the  oldest  part  of  the  clam's  shell?     Of  the  snail's? 
Read  a  description  of  the  chambered  nautilus.     Who  wrote  a  poem 
about  it? 

2.  What  is  the  economic  importance  of  the  clam?     From  what  are 
pearl  buttons  made?    What  other  materials  are  used  for  buttons? 

3.  Why  does  the  earthworm  come  to  the  surface  after  a  heavy  rain? 
Show  that  the  earthworm  is  the  "original  plowman." 

4.  Why  was  an  old-time  doctor  called  a  leech? 

5.  Give  a  list  of  at  least  5  insects  that  are  hurtful  to  man  or  to  his 
domestic  animals.    Extend  the  list,  if  you  can. 

6.  Give  a  list  of  at  least  5  insects  that  attack  food  plants  or  trees. 
Extend  the  list  if  possible. 

7.  Give  the  ways  in  which  man  protects  plants  from  the  ravages  of 
insects.     (Cf.  also  §  301.) 

8.  Why  are  insects  in  the  larva  stage  such  greedy  feeders? 

9.  Out  of  what  does  the  silkworm  spin  its  cocoon?    The  spider  its 
web?    From  what  does  the  bee  get  its  wax?    Its  honey? 

10.  How  are  insects  helpful  to  plants?     (Cf.  §  319.) 

11.  What  is   cochineal?    What  is  its  source?     Its  use?    Answer 
the  same  questions  for  sepia;  for  ambergris. 

341.  Fishes. —  The  most  striking  difference  between 
fishes  and  all  the  animals  already  studied  is  that  fishes 
have   an   interior   bony   framework   that    supports   the 


FISHES 


325 


body,  while  crustaceans,  mollusks,  etc.,  have  an  external 
hard  covering,  if  they  have  any  hard  structure  at  all. 
In  the  animals  that  are  below  fishes  in  development  the 
11  trunk  line"  of  the  nervous  system  is  in  the  lower  region 
of  the  body.  In  the  fishes  and  those  above  them  there 
is  a  spinal  cord ;  it  is  in  the  upper  region  of  the  body,  and 
it  is  protected  by  a  series  of  bones.  Each  bone  in  the 
series  is  called  a  vertebra,  and  the  whole  series  is  called 


First  Dorsal  Fin 


FIG.  266. 


Skeleton  of  a  Fish. 


the  vertebral,  or  spinal,  column  (Fig.  266).  Therefore 
fishes  and  all  higher  animals  are  called  vertebrates,  while 
the  animals  below  them  are  called  invertebrates. 

The  heart  of  the  crayfish  we  found  to  consist  of  one 
chamber,  set  in  a  space  for  receiving  the  blood  that  came 
back  from  the  body.  In  the  fish  we  find  a  heart  of  two 
chambers  (an  auricle,  which  receives  blood  from  the 
veins)  and  a  ventricle,  which  forces  blood  into  the  arteries 
(Fig.  267).  The  blood  of  fishes  is  red,  because  of  the 
presence  of  red  corpuscles  (cf.  Fig.  286,  §  378). 

The  respiration  of  the  fish  takes  place  through  gills.  In  higher 
fishes,  such  as  the  perch,  the  gills  are  all  placed  under  one  hard  cover- 
ing, back  of  the  head.  In  fishes  not  so  well  developed,  such  as  the  dog- 
fish and  shark,  there  are  gill  slits,  one  for  each  gill.  In  both  kinds  of 


326  ANIMALS 

fishes  water  is  taken  in  at  the  mouth,  and  passes  outward  through  the 
gill  openings.  This  water  contains  dissolved  oxygen  (cf.  §  52)  for 
purifying  the  blood  that  comes  to  the  gills. 

The  specific  gravity  of  a  fish  is  very  nearly  that  of  water.  An  ' '  air 
bladder"  enables  the  fish  to  change  its  specific  gravity  slightly,  and  to 
sink  or  rise  in  the  water,  much  as  a  submarine  boat  does  (cf.  §  43). 
When  it  compresses  the  air  in  the  air  bladder,  the  fish  as  a  whole 
becomes  a  little  denser,  and  goes  downward.  When  the  compressing 


Carotid 

Arterj 


FIG.  267. 
Circulation  of  Blood  in  a  Fish,  with  the  Connecting  Organs. 

muscles  are  relaxed,  the  air  expands;  thus  the  body  as  a  whole  becomes 
lighter,  and  rises. 

The  fish  moves  by  means  of  the  strokes  of  its  powerful  tail  fin,  as 
well  as  by  the  strokes  of  smaller  fins.  The  side  fins  aid  the  fish  in 
steering  itself,  while  the  fins  on  the  upper  (dorsal)  and  the  lower 
(ventral)  sides  of  the  body  keep  the  fish  right  side  up.  In  the  lower 
fishes,  such  as  sharks,  the  upper  lobe  of  the  tail  is  much  larger  than  the 
lower;  in  higher  fishes  the  tail  is  symmetrical. 

The  scales  of  fishes  form  a  hard  protective  covering.  They  lap 
over  one  another,  and  so  permit  the  body  underneath  to  bend.  Sharks 
have  a  tough  skin  covering  without  true  scales. 

342.  Amphibians. —  The  name  "  amphibians "  (pro- 
nounced am-fib'-i-ans)  comes  from  amphi,  meaning 
"both,"  and  bios,  "life";  it  refers  to  the  fact  that  amphib- 
ians live  both  on  the  land  and  in  the  water.  Examples 
of  amphibians  are  frogs,  toads,  and  salamanders. 


AMPHIBIANS 


327 


In  amphibians,  as  in  all  animals  above  them,  there  is 
not  only  a  vertebral  column,  but  there  are  four  limbs, 
the  hard  parts  of  which  are  parts  of  the  bony  skeleton. 
The  fore  legs  of  the  frog  are  small,  and  have  four  toes 
each;  the  hind  legs  are  long  and  strong,  and  each  has 
five  webbed  toes.  The  hind  legs  are,  therefore,  well 
adapted  for  both  jumping  and  swimming. 

The  frog's  body  (Fig.  268)  is  covered  with  a  colored 
skin,  the  outer  layer  of  which  it  sheds  in  moulting.  Each 


FIG.  268. 
Stages  in  the  Development  of  a  Frog. 

of  the  frog's  eyes  is  closed  by  an  upper  and  a  lower  lid; 
but  the  lower  is  the.  more  movable.  Back  of  the  eyes,  on 
the  sides  of  the  head,  are  two  membranes ;  these  form  the 
outer  ears. 

The  blood  of  amphibians,  like  that  of  fishes,  is  low  in 
temperature:  these  animals  are  "cold  blooded."  The 
heart  has  two  receiving  chambers  (a  right  and  a  left  auricle) 
and  one  ventricle.  This  is  an  advance  beyond  fishes 
(cf.  §  341). 


328  ANIMALS 

The  young  of  frogs  and  toads  undergo  a  metamorphosis  (c/.  §  339). 
As  hatched  from  the  egg  they  are  "polywogs,"  or  tadpoles.  This  is 
the  " larva"  stage.  Tadpoles  are  water  animals,  provided  with  gills 
for  breathing,  and  with  a  long  tail  for  swimming.  As  they  develop, 
the  tail  becomes  shorter,  and  the  hind  legs  appear.  The  fore  legs  are 
at  first  hidden  by  a  fold  of  the  skin  that  grows  out  to  cover  the  gills. 
The  outer  gills  disappear,  and  inner  gills  and  lungs  are  formed. 

The  tadpole  lives  upon  vegetable  food,  but  in  changing  into  an 
adult  frog  it  changes  its  diet  to,  animal  food,  chiefly  insects.  The  toad, 
although  it  is  first  a  tadpole,  leaves  the  water  entirely  when  it  grows  up. 
In  the  winter  time,  frogs  burrow  into  the  mud  at  the  bottom  of  ponds, 
and  live  there  (hibernate)  through  the  cold  weather  without  feeding. 
To  hibernate  means  to  "pass  the  winter." 

343.  Reptiles. —  Reptile  is  from  a  Greek  word  meaning 
"to  creep,"  or  "to  crawl";  the  Latin  serpo,  from  which 
"serpent"  is  derived,  means  the  same  thing.  Reptiles 
include  lizards,  chameleons,  alligators,  crocodiles,  turtles, 
and  snakes. 

Reptiles,  like  amphibians,  are  cold-blooded;  but  they 
differ  from  amphibians  in  that  they  breathe,  from  the 
first,  with  lungs.  The  heart  of  the  crocodiles  is  higher  in 
development  than  that  of  other  reptiles,  for  it  has  two 
auricles  (receiving  chambers)  and  two  separate  ventricles 
(chambers  from  which  blood  is  pumped  to  the  body  and 
the  lungs).  In  this  respect  crocodiles  are  like  birds  and 
mammals,  including  man  (cf.  §  375).  Other  reptiles  are 
like  amphibians.  When  there  are  two  ventricles,  the 
pure  blood  from  the  lungs  and  the  impure  blood  from  the 
body  are  not  mixed  in  the  heart. 

Reptiles  are  covered  with  horny  or  with  bony  plates,  or 
both.  The  horny  plates  come  from  the  outer  skin,  and 
are  usually  "shed"  and  renewed,  as  in  the  case  of  snakes. 


BIRDS 


329 


Lizards  have  long  bodies  with  a  distinct  head,  neck,  and 
tail.  Their  feet  have  five  toes  each.  Turtles  have  a 
peculiar  form,  and  move  slowly,  because  of  their  protective 
box  of  horny  material.  In  temperate  climates,  reptiles 
hibernate  in  winter. 

Snakes  have  the  remains  of  bones  which  show  that  their  ancestors 
once  had  limbs;  but  modern  snakes  have  no  limbs.  In  spite  of  this 
they  move  rapidly.  The  body  of  the  snake  is  so  narrow  that  there  is 
little  room  for  some  of  its  internal  organs,  so  these  are  altered.  Thus, 
one  lung  is  very  small,  and  almost  useless.  On  the  other  hand,  the 
long  muscular  body  is  a  wonderful  structure  for  the  seizing  and  crush- 
ing of  prey.  Most  small  snakes  are  harmless.  The  dangerous  ones  in 
this  country  are  rattlesnakes,  water  moccasins,  and  copperheads.  In 
India  there  is  a  great  python,  and  in  South  America,  the  anaconda, 
which  grows  to  a  length  of  30  feet.  These  kill  their  prey  by  crushing  it. 

Reptiles  reached  an  enormous  size  in  past  geological  times,  as  their 
fossils  tell  us.     There  were  then 
swimming,    walking,    and    flying 
reptiles. 

344.  Birds. — In  certain 
rocks  there  have  been  found 
the  remains  (fossils)  of  birds 
that  are  remarkably  like 
reptiles.  They  have  a  long, 
jointed  tail,  as  reptiles  have, 
and  the  tail  feathers  come  in 
pairs  from  these  joints.  In 
modern  birds  (Fig.  269)  the 
tail  joints  are  so  much  short- 
ened that  all  the  feathers 
seem  to  come  from  one  place. 


Sternum 


FIG.  269. 
Skeleton  of  a  Bird. 


These  fossil  birds  had  teeth 


like  those  of  reptiles ;  modern  birds  have  only  a  horny  beak 


330 


ANIMALS 


formed  out  of  skin.  In  the  ancient  bird,  the  wing  was 
much  like  a  simple  fore  limb,  instead  of  the  greatly  altered 
structure  that  we  see  in  the  wings  of  modern  birds. 

While  modern  birds  still  have  some  of  the  charac- 
teristics of  reptiles,  .in  other  respects  they  have  gone  far 
beyond  them.  Instead  of  being  cold-blooded,  birds  have 
a  higher  blood  temperature  than  any  other  animal;  viz., 
from  100°  F.  to  110°  F.  Man's  blood  is  at  98.6°  F. 
Horny  scales,  which  cover  reptiles,  appear  only  on  the 
legs  and  feet  of  birds,  while  the  main  portion  of  the  body 
is  covered  with  feathers.  In  flying  birds  the  body  is 
wonderfully  fitted  for  flight;  in  wading  birds  the  neck 
and  feet  are  long;  while  in  the  case  of  swimming  birds  the 
feet  are  webbed.  The  foot  of  a  bird  usually  has  four 
toes.  In  climbing  birds  two  of  the  toes  are  directed 
forward  and  two  backward.  In  perching  birds  three 

toes   are  directed  forward, 
and  one  backward. 


Crop 


Pelvis 


Stoma 


The  gullet  of  birds  is  enlarged 
into  a  crop  for  the  storing  of  food 
(Fig.   270).     The  gizzard  is   the 
muscular  part  of  the  stomach.     In 
grain-eating  birds  the  inner  lining 
of  the  gizzard  is  hard  and  rough. 
This  rough  lining,  together  with 
the  gravel  and  sand  which  these 
birds  eat,  takes  the  place  of  teeth 
in  grinding  and  crushing  the  food. 
The  brain  and  the  nervous  system  of  birds  are  highly  developed. 
We  ought  to  expect  this  from  the  wonderful  ways  in  which  birds  adapt 
themselves  to  their  surroundings,  and  from  the  great  care  that  they 
give  to  their  young. 


Sternurq 


Intestine 

FIG.  270. 
Digestive  System  of  a  Bird. 


MAMMALS 


331 


Much  has  been  written  of  the  usefulness  of  wild  birds  to  man,  and 
this  usefulness  can  hardly  be  exaggerated.  Perhaps  their  greatest 
service,  aside  from  the  pleasure  they  give  us,  is  in  the  destruction  of 
insects  that  attack  our  food  plants  and  trees. 

345.  Mammals. —  Mammals  are  so  called  because  they 
produce  milk  to  nourish  their  young.  The  young  are 
brought  forth  alive,  but  require  a  period  of  care  before  they 
are  mature.  While  reptiles  have  a  covering  of  plates,  and 
birds  one  of  feathers,  the  skin  of  mammals  forms  a  covering 
of  hair.  The  nails,  claws,  hoofs,  and  horns  of  animals, 
including  the  quills  of  the  porcupine,  are  all  modified  hair. 

Mammals  are  all  air-breathing,  and  live  chiefly  on  the 
land.  Whales  and  porpoises  are  mammals  that  live  in 
the  sea.  The  whale  has  lost  its  hind  limbs,  although  there 
are  remnants  of  them  under  the  surface  of  its  body.  The 
whale's  front  limbs  have 
been  changed  to  flaps, 
to  meet  its  needs  as  a 
swimmer.  The  bat,  also 
a  mammal,  has  learned 
to  fly. 

A  strange  creature,  the 
duckbill,  which  lives  in 
Australia,  is  like  birds 
and  reptiles,  on  the  one 
hand,  and  like  mammals, 
on  the  other.  It  lays 
eggs,  but  it  also  forms  Fll27i  , 

An  Opossum.    The  Field  Museum. 

milk  for  its  young.     One 

group  of  mammals  includes  kangaroos  and  opossums  (Fig. 

271).     These  bring  forth  their  young  alive,  but  the  young 


332  ANIMALS 

are  very  feeble  and  immature.  The  mother  therefore 
keeps  them  in  a  pouch  made  of  a  fold  of  her  skin,  and 
nurtures  them  with  milk  until  they  have  become  strong. 

The  nervous  system  of  mammals  is  developed  more  highly  than  in 
other  animals.  This  is  especially  true  of  the  size  of  the  brain,  and  of 
the  folding  of  its  surface.  The  folding  increases  the  brain's  area,  and, 

therefore,  its  capacity  for  de- 
Esophagus    (Tf 

velopment. 

The  digestive  organs  of 
mammals  (Fig.  272)  consist  of 
the  mouth,  gullet,  stomach, 
and  intestines  (bowels),  with 
many  glands  (cf.  §  358),  such 
as  the  liver.  The  structure  of 
Digestive  organs  of  a  Cow.  the  stomach  is  very  different 

for    different    mammals.     In 

herb-eating  animals,  such  as  the  sheep  and  the  cow,  the  stomach  has  a 
lobe,  or  paunch,  in  which  food  can  be  stored.  This  storage  stomach  of 
the  ox  holds  about  two  bushels.  After  the  animal  stops  its  feeding, 
the  food  returns  to  the  mouth,  and  is  chewed  more  finely  (' '  chewing 
of  the  cud").  Then  the  food  passes  on  to  the  true  stomach.  Flesh- 
eating  (carnivorous)  animals  have  a  much  simpler'  stomach  and  a 
shorter  intestine  than  herb-eating  (herbivorous)  animals,  because  their 
food  requires  less  space  for  digestion. 

346.  Classes  of  Animals. —  In  Chapter  XV  we  learned 
that  we  can  put  all  known  plants  into  groups,  or  classes, 
according  to  the  way  in  which  each  kind  of  plant  meets 
and  solves  the  great  problems  of  food  getting,  growth,  and 
reproduction.  In  the  present  chapter  we  have  learned 
that  we  can  classify  animals  in  a  similar  way.  Just  as 
we  trace  the  steps  of  development  from  the  protococcus 
to  the  daisy,  so  we  can  trace  the  steps  from  the  ameba  to 
mammals.  The  ameba  is  as  truly  alive  as  a  horse;  why 


CLASSES  OF  ANIMALS  333 

then  do  we  think  of  it  as  a  low  animal?  The  answer  is 
that  the  horse  has  wonderful  and  special  organs  for  par- 
ticular duties,  while  the  ameba  has  only  one  cell  for  all  its 
functions.  In  the  ameba  the  cell  is  entirely  independent 
of  other  cells;  in  the  mammal  each  cell  has  given  up  part 
of  its  independence  in  order  that  a  multitude  of  cells  may 
live  together. 

When  many  cells  live  together  in  an  organism,  each 
cell  does  not  need  to  carry  out  all  the  functions  of  the 
organism;  for  there  is  a  "division  of  labor"  among  the 
cells,  just  as  there  is  among  the  workmen  of  a  successful 
factory.  We  saw  the  beginnings  of  this  "division  of 
labor"  in  the  case  of  the  hydra  (cf.  §  334).  As  we  ascend 
the  scale  of  animal  forms,  we  find  the  division  of  labor 
becoming  more  complete.  Thus,  the  problem  of  food 
digestion  is  worked  out  in  a  more  and  more  excellent  way. 
The  circulation  of  the  blood,  which  begins  in  the  con- 
traction of  some  part  of  the  blood  tubes  of  an  earthworm, 
ends  in  the  four-chambered  heart  of  birds  and  mammals. 
Respiration  is  first  carried  o'ut  by  all  the  cells;  then  by 
some  cells  that  have  thinner  walls.  In  higher  creatures 
these  thin  walls  are  greatly  folded,  so  that  they  shall  have 
a  large  surface,  and  the  result  is  the  gill  structure.  In 
amphibians  we  see  the  change  from  gills  to  lungs,  while  in 
reptiles,  birds,  and  mammals  gills  are  not  used  at  all. 

We  are  likely  to  think  that  the  mammals  now  on  the  earth  have 
always  had  their  present  forms.  That  this  is  not  true  is  admirably 
illustrated  by  the  case  of  the  horse.  The  fossils  of  the  first  horse  show 
that  the  animal  was  of  about  the  size  of  a  fox,  and  that  it  had  five 
toes  to  each  foot.  But  the  succession  of  fossils  shows  that  the  first 
and  fifth  toes  became  mere  splints,  producing  a  three-toed  animal  as 


334  ANIMALS 

large  as  a  sheep.  Then  the  second  and  fourth  toes  became  splints, 
while  the  splints  of  the  first  and  fifth  toes  disappeared  entirely.  This 
is  the  condition  in  the  modern  horse.  Its  hoofs  are  the  enlarged  nails 
of  the  third  (middle)  toe,  and  there  are  splints  that  represent  the  second 
and  fourth  toes. 

347.  Importance  of  Animals  to  Man. —  Primitive  men 
seem  to  have  lived  upon  the  fruits,  seeds,  and  roots  of 
wild  plants,  and  upon  insects,  worms,  and  small  reptiles. 
But  when  they  invented  weapons  and  tools,  they  were 
able  to  kill  large,  wild  animals,  and  to  live  upon  meat. 
It  was  an  important  day  when,  with  traps  and  snares, 
men  began  to  capture  animals  alive;  for  they  then  began 
the  process  of  domesticating  animals.  The  people  of 
Europe  and  Asia  certainly  learned  to  keep  cattle,  goats, 
sheep,  horses,  and  chickens,  very  long  ago.  As  these 
animals  were  protected  by  man,  they  gradually  lost  many 
of  their  wild  habits,  and  man,  too,  in  depending  upon 
them,  largely  lost  his  need  of  hunting  wild  game.  It  was 
natural,  however,  that  men  living  near  the  ocean  or 
inland  waters  should  continue  to  catch  water  animals, 
such  as  fish,  oysters,  and  lobsters,  and  these,  especially 
fish,  still  form  the  food  of  a  large  portion  of  the  human 
race. 

Man  learned  to  use  his  domestic  animals  not  only  for 
their  meat  and  milk,  but  also  to  carry  himself  and  his 
loads.  To  give  his  animals  and  himself  a  more  certain 
supply  of  vegetable  food,  he  cultivated  grains,  fruits,  etc. 
As  a  result,  he  was  able  to  cease  his  wandering  over  the 
earth  in  search  of  pasturage,  and  to  settle  down  upon 
farms.  Strangely  enough,  the  horse  probably  originated 
upon  the  American  continent,  but  became  extinct  here 


SUMMARY  335 

before  man  could  use  it.  The  ancestors  of  all  the  horses 
in  America  have  been  brought  here,  from  Europe  or  Asia, 
since  the  days  of  Columbus.  One  reason  why  man's 
progress  was  far  more  slow  in  America  than  in  Europe 
and  Asia  may  have  been  that  there  were  no  beasts  here 
that  could  be  readily  domesticated  as  helpers  of  man. 

Man  has  developed  all  the  different  varieties  of  chickens,  dogs,  cats, 
pigeons,  etc.,  as  he  has  developed  the  .varieties  of  domestic  plants; 
namely,  by  selecting  the  individuals  that  possessed  certain  qualities 
that  he  desired,  and  then  breeding  these  individuals,  generation  after 
generation,  so  as  to  make  the  desired  qualities  more  and  more  promi- 
nent. Thus  horses  are  bred  for  different  purposes,  such  as  for  racing, 
for  ordinary  driving,  for  hauling  loads  in  the  city,  and  for  farm  work. 
The  horse  that  is  good  for  one  of  these  uses  is  not  necessarily  good  for 
any  of  the  others.  The  types  of  cattle  wanted  for  the  commercial 
production  of  milk  and  butter  are  different  from  those  wanted  for 
meat.  Sheep  may  be  bred  for  the  quality  of  their  wool  or  the  quality 
of  their  flesh.  Breeds  of  chickens  that  lay  well  are  often  unprofitable 
as  meat  producers.  The  growth  of  scientific  knowledge  in  the  last 
50  years  has  greatly  increased  the  efficiency  of  animal  breeding. 

348.  Summary. —  Animals  cannot  build  up  their  food  out  of  mineral 
matter ;  plants  containing  chlorophyll  can. 

In  the  ameba  a  single  cell  can  carry  out  the  necessary  animal  func- 
tions. 

The  hydra  consists  of  two  layers  of  cells  which  have  slightly  differ- 
ent functions.  Each  cell  can,  however,  take  up  all  the  functions  if 
necessary. 

Starfishes  are  much  more  highly  developed  than  hydras.  They 
have  the  beginnings  of  a  nervous  system,  a  digestive  system,  a  blood 
system,  a  breathing  system,  and  of  organs  of  smell  and  of  sight. 

Worms  have  more  symmetry  than  starfishes,  and  more  highly 
developed  organs.  Earthworms  are  of  enormous  value  to  the  soil, 
since  they  prepare  it  for  plant  growth. 

Mollusks  include  oysters,  clams,  snails,  slugs,  and  the  octopus. 


336  ANIMALS 

Crustaceans  include  crayfishes,  lobsters,  crabs,  and  barnacles. 
They  have  three  body  regions:  head,  thorax,  and  abdomen.  The 
crayfish  has  a  one-chambered  heart  and  arteries,  but  no  veins.  Res- 
piration is  by  gills. 

Insects  also  have  three  body  regions.  Respiration  is  in  air  passages, 
and  not  in  gills.  When  insects  undergo  metamorphosis,  there  are 
usually  three  stages:  the  larva,  pupa,  and  adult  stages.  Insects 
(including  spiders)  form  the  most  numerous  class  of  animals. 

Fishes  and  all  animals  above  them  are  called  vertebrates.  They 
have  a  spinal  cord  and  an  interior  bony  framework.  All  animals  below 
fishes  are  called  invertebrates.  The  heart  of  the  fish  is  two-chambered, 
its  blood  is  red,  and  its  gills  are  well  developed. 

Amphibians  have  limbs,  and  live  partly  on  land  and  partly  in 
water.  Frogs  and  toads  hatch  out  as  tadpoles.  The  heart  of  am- 
phibians has  two  auricles  and  one  ventricle.  The  adult  breathes 
with  lungs. 

Reptiles  breathe  only  with  lungs.  The  body  is  covered  with  horny 
plates.  The  highest  reptiles,  the  crocodiles,  have  a  four-chambered 
heart. 

Birds  show  a  great  advance  over  reptiles,  but  have  some  reptilian 
qualities.  Their  blood  is,  however,  warm.  The  brain  and  nervous 
system  are  highly  developed.  The  body  is  covered  with  feathers. 

Mammals  have  a  covering  of  hair,  and  bring  forth  their  young  alive. 
They  are  all  air  breathers.  The  brain  and  nervous  system  are  the 
highest  among  animals.  Most  mammals  are  either  herbivorous  or 
carnivorous.  Man  is  omnivorous;  that  is,  he  eats  both  vegetable  and 
animal  food. 

The  high  development  of  animals  is  due  to  the  ' '  division  of  labor ' ' 
among  the  cells. 

Man  has  had  a  great  influence  in  the  development  of  economic 
animals,  and  animals  have  had  a  powerful  influence  on  the  develop- 
ment of  man. 

349.  Exercises. 

1.  Name  some  invertebrates  that  are  used  as  food  by  man.  Which 
is  the  most  important  in  this  respect?  Are  any  amphibians  used  as 


EXERCISES  337 

food?    Any  reptiles?    Which  class  of  mammals  does  man  use  as  food, 
the  carnivorous  or  the  herbivorous  animals? 

2.  Find  out  about  how  many  eggs  your  family  uses  weekly  and 
annually.  Find  out  how  many  your  city  uses,  and  where  the  supply 
comes  from. 

3.  To  what  uses  did  primitive  man  put  the  skins  and  furs  of  ani- 
mals?   Name  several  of  the  ways  in  which  we  use  them  to-day. 

4.  How  has  the  camel  been  useful  to  man?    The  reindeer?     The 
dog?    How  is  the  cat  helpful  to  man?    How  is  it  injurious? 

5.  The  Latin  word  for  money,  pecunia,  from  which  we  get  our  word 
" pecuniary,"  comes  from  a  word  meaning  "cattle."     How  did  this 
come  about? 

6.  How  have  the  tendons  of  animals  (cf.  §  355)  been  used  by  man? 
The  bones?    The  horns? 

7.  What  is  ivory?    For  what  is  it  used?    What  is  the  modern 
substitute  for  it? 

8.  What  is  sperm  oil,  and  for  what  is  it  used? 

9.  What  is  the  source  of  the  bristles  of  brushes?     Did  the  Indian 
have  any  use  for  the  porcupine's  quills?    What  other  uses  has  man 
for  the  hair  of  animals? 

10.  Name  some  economic  products  obtained  from  birds,  aside  from 
their  eggs  and  flesh. 

11.  What  is  the  source  of  glue?    Of  gelatine? 

12.  Name   several   climbing   birds.    Perching   birds.     Swimming 
birds.     Wading  birds. 

13.  Ask  a  farmer  or  a  liveryman,  if  you  do  not  know,  why  horses 
are  fed  oats  in  addition  to  hay  or  grass. 

14.  Name  some  economic  uses  of  fishes  aside  from  the  use  of  their 
flesh  as  food. 


CHAPTER    XVII 
THE  HUMAN  BODY  AND  ITS  FOOD 

350.  Chief  Divisions  of  the  Body. —  The  science  that 
deals  with  the  organs  of  plants  and  animals,  and  with  the 
functions  of  these  organs,  is  called  Physiology.  The 
science  of  the  human  body  is  called  Human  Physiology. 
In  Chapter  XVI  we  learned  that  while  in  animals  below 
fishes  (invertebrates)  the  parts  supporting  the  body,  if 
there  are  any,  are  on  the  outside  of  the  body,  in  fishes  and 
the  animals  above  them  (vertebrates)  the  framework  of 
the  body  is  on  the  inside,  and  takes  the  form  of  a  bony 
skeleton.  Along  with  this  change  in  the  body  framework 
there  is  also  a  change  in  the  position  of  the  nervous  sys- 
tem; in  the  vertebrates  the  important  nerve  centers  are 
all  on  the  dorsal  side  (the  back).  We  therefore  think  of 
the  body  of  a  fish  as  having  two  spaces,  or  cavities:  (1)  a 
dorsal  cavity,  consisting  of  the  brain  space  (skull)  and 
the  long  narrow  space  (canal)  inside  the  spinal  column; 
and  (2)  a  ventral  cavity.  The  ventral  cavity  is  much  the 
larger,  and  contains  the  organs  of  respiration,  circulation, 
digestion,  etc. 

In  mammals  we  make  the  same  body  divisions  as  in  the 
fish,  but  we  divide  the  ventral  cavity  into  two  distinct 
parts:  (1)  the  thorax,  and  (2)  the  abdomen. 

The  diaphragm  forms  the  dividing  wall  between  these 
two  parts.  In  man  (Fig.  273)  these  same  divisions  exist. 
The  thorax  contains  the  lungs,  the  heart,  some  large 

338 


CELLS  AND  TISSUES  OF  THE  BODY 


339 


blood  vessels,  and  the  esophagus,  by  which  food  is  carried 
from  the  mouth  to  the  stomach.  Below  the  diaphragm  is 
the  abdomen,  which  contains  the  stomach,  intestines 
(bowels),  liver,  kid- 
neys, pancreas,  spleen, 
etc.  The  thorax  and 
abdomen  together 
form  the  trunk. 

351.  Cells  and  Tis- 
sues  of  the  Body.— 

The  human  body,  like 
that  of  any  plant  or 
animal,  is  composed 
of  cells.  These  cells 
are  living,  and  con- 
sist of  cell  walls  and 
protoplasm  (cf.  §  323). 
Like  the  ameba  (cf. 
§  333)  they  carry  on 
the  fundamental  pro- 
cesses of  life.  They 
feed,  and  they  reject 
the  waste  from  their  food.  They  also  reproduce  them- 
selves by  the  process  of  cell-division  (cf..  §  323).  Unlike 
the  cells  formed  by  the  division  of  an  ameba,  however, 
the  new  cells  of  our  bodies  do  not  separate  from  the  old 
ones,  but  remain  together.  In  this  way  the  whole  body 
can  grow,  and  new  cells  can  at  once  replace  those  that  die. 

Since  the  cells  of  our  bodies  form  a  large  community,  the  division 
of  labor  is  necessary  (cf.  §  346).     Hence  we  find  special  groups  of  cells 


FIG.  273. 
The  Principal  Organs  of  the  Thorax  and  the  Abdomen. 


340  THE  HUMAN  BODY  AND  ITS  FOOD 

set  apart  to  do  special  kinds  of  work.  A  group  of  cells  in  which  all 
the  cells  do  the  same  kind  of  work  is  called  a  tissue.  Out  of  certain 
tissues,  or  mixtures  of  tissues,  the  organs  of  the  body  are  made.  The 
muscles  contain  muscle  tissue,  or  groups  of  muscle  cells,  and  nerves 
contain  nerve  tissue,  which  consists  of  nerve  cells. 

One  form  of  tissue  is  called  connective  tissue,  because  it  connects 
other  cells.  Its  cells  have  slender,  fine  branches  which  extend  between 
the  other  cells,  and  hold  all  together.  So  muscles  really  consist  of 
muscle  tissue  held  together  by  connective  tissue. 

352.  Structure  of  Bones. —  Bones  are  made  up  of 
branching,  interlaced  cells  of  connective  tissue,  stiffened 
with  limestone  and  calcium  phosphate  (cf.  §  302).  The 
limestone  is  about  %  of  the  weight  of  the  bone.  Among 
the  bone  cells  there  are  tubes,  or  "canals,"  containing 
blood  vessels  and  nerves.  The  outside  layer  of  a  bone  is 
very  compact,  and  the  whole  bone  has  a  tough  covering 
of  connective  tissue.  This  is  called  the  periosteum, 
meaning  "around  the  bone."  The  animal  matter  (that 
is,  the  connective  and  other  tissues)  of  a  bone  may  be 
destroyed  by  burning.  The  ashes  will  contain  the 
mineral  part.  The  limestone  we  can  remove  by  soaking 
the  bone  in  some  dilute  acid,  such  as  dilute  hydrochloric 
acid  (cf.  §  128).  The  tough  connective  tissue  will  remain, 
but  the  stiffening  will  be  gone.  Long  bones  have  cavities. 
They  thus  give  the  greatest  possible  strength,  with  the 
least  possible  weight. 

Cartilage  is  pliable,  immature  bone.  It  contains  very  little  lime- 
stone, and  forms  the  skeletons  of  young  animals.  As  limestone  is 
added,  bones  become  more  hard,  but  also  more 'brittle.  However,  all 
the  cartilage  in  the  body  does  not  become  hardened.  Some  remains 
at  the  end  of  almost  every  bone,  to  diminish  friction,  and  to  prevent 
the  jarring  of  one  bone  against  another. 


JOINTS 


341 


Pelvis 


353.  Joints. —  A  joint  is  a  place  where  bones  come  to- 
gether. Some  joints  are  intended  to  be  bent  freely; 
these  are  called  flexible,  or  movable,  joints.  Some  joints 
are  not  arranged  for  bending;  these  are  inflexible,  or  im- 
movable, joints.  Some  of  the  bones  of  the  skull  are  held 
together  in  inflexible  joints. 

Between  inflexible  joints  there  is  usually  a  layer  of 
cartilage  or  of  material  much  like  it.  Its  use  is  shown 
admirably  in  the  backbone,  where  it  forms  pads  between 
the  vertebrae.  These  pads  permit  the  backbone  to  be 
bent  somewhat,  and 
act  as  cushions  to 
relieve  the  skull  as 
much  as  possible 
from  the  jar  caused 
by  walking  and 
running. 

At  movable  joints 
the  bones  are  held 
together  by  tough 
bands,  called  liga- 
ments, and  the  ends 

of  the  bones  are  smooth  and  round.  When  muscles 
pass  over  joints,  they  also  assist  in  holding  the  bones 
together.  We  distinguish  three  principal  kinds  of  mov- 
able joints  (Fig.  274)  :— 

(1)  Those  in  which  the  movement  is  in  two  opposite  direc- 
tions only,  as  in  an  ordinary  hinge;  these  are  called  hinge 
joints.     The  knees,  elbows,  and  fingers  have  hinge  joints. 

(2)  Those  that  can  be  moved  in  any  direction,  as  the 
arm  can  at  the  shoulder.     Such  joints  have  the  rounded 


Patella 


FIG.  274. 
A  Hinge  Joint  and  a  Ball-and-Socket  Joint. 


342 


THE  HUMAN  BODY  AND  ITS  FOOD 


I  Bone 


FIG.  275. 
The  Skeleton  and  its  Parts. 


end  of  one  bone 
fitting  into  the 
socket  of  another, 
and  are  called 
ball-and-socket 
joints. 

(3)  Those  in 
which  one  bone 
glides  over  an- 
other; these  are 
called  gliding 
joints. 

354.  The  Skele- 
ton.— The  human 
skeleton  -(Fig. 
275)  consists  of 
206  bones,  which 
together  form  the 
frame  work  of  the 
head,  trunk,  and 
limbs.  The  bones 
of  the  head  make 
up  the  skull. 
The  cranium,  or 
"brain  box,"  is 
made  up  of  8  bony 
plates  joined  to 
gether.  The  face 
is  supported  by 
14  '  :nes,  and 


THE  SKELETON 


343 


Emensors 
of  Fingers 


there  are  3  little  bones  in  each  ear.     This  makes  a  total 
of  28  bones  in  the  head. 

The  backbone,  or  spinal  column,  consists  of  24  bony 
rings,  or  vertebrae  (cf.  §  341).  There  are,  in  addition, 
two  bones  at  the  base  of 
the  backbone;  these  are 
called  the  sacrum  and  the 
coccyx. 

Twelve  of  the  vertebrae 
have  2  ribs  each.  The  7 
upper  pairs  of  ribs  are 
joined  in  front  to  the 
sternum,  or  breast  bone, 
and  are  called  true  ribs. 
The  5  lower  pairs  of  ribs 
are  called  false  ribs.  The 
3  upper  pairs  of  false  ribs 
are  joined  to  the  lowest 
pair  of  true  ribs.  The  2 
lowest  pairs  of  false  ribs 
are  not  attached,  in  front, 
to  anything,  and  are  called 
floating  ribs.  The  shoulder 
bones  are  2  clavicles  (collar 
bones)  and  2  scapulas 
(shoulder  blades).  There 
is  also  a  hyoid  bone  at  the 
base  of  the  tongue.  The 
lower  end  of  the  abdomen 
is  supported  by  the  sacrum  and  coccyx  bones  of  the 
spinal  column,  and  by  the  2  pelvic,  or  hip,  bones. 


FIG.  276. 
Surface  Muscles  of  the  Body. 


344  THE  HUMAN  BODY  AND  ITS  FOOD 

These  4  bones  form  the  pelvis.     There    are    altogether 
58  bones  in  the  trunk. 

The  four  limbs  have  30  bones  each.  Each  arm  has  a  humerus 
(upper  arm),  radius  and  ulna  (lower  arm),  8  wrist  bones  (carpals),  5 
hand  bones  (metacarpals) ,  and  14  finger  bones  (phalanges).  Each 
leg  has  a  femur  (thigh  bone) ,  and  a  tibia  (shin  bone)  and  a  fibula  below 
the  knee.  At  the  front  of  the  knee  is  the  knee  cap  (patella).  In  the 
ankle  there  are  7  tarsal  bones;  in  the  foot,  5  metatarsals;  in  the  toes, 
14  phalanges. 

A  summary  of  the  list  of  bones  is  as  follows : — 

Bones  of  Head. 

Cranium 8          Sternum 1 

Face -  14          Hyoid 1 

Ears 6          Clavicles-  - 2 

Scapulas      2 

28 

58 
Bones  of  Trunk.  Bones  of  Limbs. 

Vertebrae 24          Upper  limbs 60 

Pelvis   --------    4          Lower  limbs 60 

Ribs 24 

120 
Total  Number  of  Bones  206 

355.  Muscles  and  Tendons. —  The  muscles  are  the 
organs  that  move  the  animal  body  (Fig.  276),  and  at  the 
same  time  cover  the  skeleton  with  rounded  flesh.  They 
constitute  the  lean  part  of  meat.  Muscles  are  made  up  of 
long  cells.  Connective  tissue,  in  the  form  of  a  white, 
skin-like  membrane,  is  present  between  the  muscle  cells, 
and  also  holds  the  muscles  in  bundles. 

The  business  of  muscles  is  to  grow  shorter  (to  contract) 
when  commanded.  By  the  shortening  of  all  the  cells, 


MUSCLES  AND  TENDONS  345 

the  muscle  itself  grows  shorter.  At  a  movable  joint  two 
muscles  usually  act  in  opposition  to  each  other,  like  two 
springs  on  opposite  sides  of  a  door.  If  one  muscle 
shortens  itself,  the  other  grows  longer.  The  two  give  a 
forward  and  backward  motion  to  the  bone,  like  that 
which  we  see  when  we  raise  and  lower  the  forearm. 

Tendons  are  the  extensions  of  the  connective  tissue 
of  muscles;  they  bind  muscles  to  bones.  The  tendons 
are  sometimes  very  long,  and  attach  a  muscle  to  a  bone 
at  a  distance.  This  is  true  in  the  hand.  The  thick 
muscles  that  move  the  hand  are  in  the  forearm,  while  the 
hand  itself  is  slender  and  skillful.  The  long  tendons  that 
extend  to  the  hand  and  the  foot  are  held  down,  near  the 
bones,  by  means  of  circular  bands  (ligaments)  at  the 
wrist  and  ankle. 

The  bones  act  as  levers  (cf.  §§198  and  199).  The  fulcrum  is  the 
joint.  The  weight  is  the  member  that  is  moved,  and  whatever  it  holds. 
The  power  is  the  pull  produced 
by  the  end  of  the  muscle  or 
tendon  at  the  place  where  it  is 
attached  to  the  bo'ne.  To  lift 
your  forearm  (Fig.  277)  the  biceps 
muscle  of  the  upper  arm  (Fig.  276) 
contracts,  and  pulls  upon  the 
radius  bone  a  few  inches  below 
the  elbow.  The  power  is  be- 
tween the  fulcrum  and  the  weight;  Fulcru 
hence  this  is  a  lever  of  the  third  FlG  2?7. 

claSS.      Most  of  the  levers  in   the    A  Third  Class  Lever  in  the  Arm.     The  power 
.,,.,,  is  supplied  by  the  contraction  of  the  biceps 

body  are  of  the  third  class.  muscle. 

Some  muscles  are  under  the  control  of  the  will  (vol- 
untary muscles),  and  some  are  not  (involuntary  muscles). 


346  THE  HUMAN  BODY  AND  ITS  FOOD 

Our  bodies  carry  out  the  functions  of  digestion  and  circu- 
lation without  our  wills:  the  muscles  of  heart  and  stom- 
ach do  not  require  our  attention.  But  if  you  wish  to 
throw  a  baseball,  or  to  "  drive"  a  golf  ball,  or  to  sew  or 
write,  your  brain  must  call  upon  certain  muscles  to  pro- 
duce the  proper  motions.  The  body  is  held  erect,  and 
the  joints  are  prevented  from  collapsing  by  the  action  of  a 
multitude  of  muscles. 

356.  Injuries  to  Bones  and  Muscles. —  When  bones  are 
broken,  it  is  not  only  the  mineral  matter  that  breaks,  but 
the  connective  tissue,  and  the  blood  tubes  and  nerves  as 
well.  When  the  broken  pieces  are  held  together  by 
bandages  and  splints,  new  cells  of  connective  tissue  unite 
the  broken  edges,  and  restore  the  connections  of  the 
nerves  and  blood  vessels.  The  filling  of  the  connective 
tissue  with  minerals  is  the  slowest  part  of  the  healing 
process.  When  this  takes  place,  the  bone  is  said  to 
"knit"  together.  As  a  person  grows  older,  more  mineral 
is  deposited  in  the  bones,  and  they  become  more  brittle. 
They  therefore  break  more  easily  than  in  childhood,  and 
do  not  unite  so  readily  if  broken. 

When  the  bones  of  a  joint  are  separated,  the  bones  are 
said  to  be  dislocated,  or  "out  of  joint."  In  this  case  the 
ligaments  and  muscles  at  the  joint  are  probably  torn. 
In  a  bad  dislocation  the  muscles  may  draw  up  the  bones 
and  prevent  them  from  going  back  into  place  for  some 
time.  The  physician  then  puts  splints  on  the  joint  to 
hold  it  stiff  until  the  ligament  has  time  to  grow  together 
again.  The  chief  difference  between  a  sprain  and  a  dis- 
location is  that  in  a  sprain  the  bones  are  not  separated. 


KINDS  OF  FOOD  347 

Tuberculosis    (consumption)    often   attacks   the   joints. 
At  the  hip  it  produces  "hip  disease. " 

The  chief  injuries  to  muscles  come  from  either  overwork  or  under- 
work. Most  students  take  too  little  exercise,  and  are  content  to  let 
others  play,  while  they  themselves  look  on.  The  body  should  get 
daily  exercise,  best  out  of  doors.  One  should  exercise  until  he  just 
begins  to  be  a  little  tired;  then  he  should  rest.  By  gradually  increasing 
the  amount  of  our  exercise,  all  of  us  can  build  up  vigorous  bodies.  But 
exercise  is  useless  unless  we  have  good  food,  and  long  hours  of  sleep,  and 
unless  we  avoid  alcohol  and  all  other  harmful  stimulants. 

357.  Kinds  of  Food. —  As  the  cells  of  the  body  do  their 
work,  some  of  their  protoplasm  is  used  up,  and  needs  to 
be  replaced.  Moreover,  as  the  oxygen  of  the  blood 
comes  to  the  cells,  it  "burns  up"  (oxidizes)  some  of  the 
cell  material  to  give  energy  to  the  cells.  There  are, 
therefore,  two  distinct  reasons  why  we  must  have  food : 

(1)  In  order  to  give  the  cells  material  for  their  growth 
and  repair; 

(2)  In  order  to  give  them  energy,  so  that  they  can  do 
their  work. 

So  we  may  say  that  anything  which  gives  the  body  the 
materials  for  growth  and  repair,  or  which  gives  it  heat  or 
energy,  is  food. 

In  spite  of  the  fact  that  we  eat  many  foods,  we  can  re- 
duce the  kinds  of  food  to  five  simple  foods,  or  nutrients 
(Fig.  277a;  also  Appendix,  Table  XII).  The  nutrients  are: 

1.  Proteids.  4.  Minerals. 

2.  Carbohydrates.  5.  Water. 

3.  Fats. 

Proteids  are  obtained  from  both  animal  and  vegetable 
food  (cf.  §§  56,  298,  and  299).  One  form  of  proteids  is 


348 


THE  HUMAN  BODY  AND  ITS  FOOD 


albumin,  present  in  the  whites  of  eggs;  another  form  is 
casein,  present  in  cheese  and  milk.  A  third  proteid  is 
gluten,  found  in  wheat  and  other  grains;  a  fourth  is 


Potato 


Sirloin  Steak 


Egg  White  Bread 

FIG.  277a. 
Nutrients  in  Some  Common  Foods. 

legumen,  found  in  beans,  peas,  and  peanuts.  Myosin,  a 
fifth  proteid,  is  abundant  in  lean  meat  (muscles).  Pro- 
teids  contain  chiefly  carbon,  hydrogen,  oxygen,  nitrogen, 
sulphur,  and  sometimes  phosphorus.  They  are  easily 


KINDS  OF  FOOD  349 

changed  to  protoplasm  by  the  cell,  and  are  used  especially 
for  the  building  up  and  repairing  of  the  body  tissues. 
Proteids  give  off  some  energy  when  oxidized,  but  other 
nutrients  are  better  for  this  purpose. 

Gelatine  is  extracted  from  bones  when  they  are  boiled  with  water. 
Like  the  proteids,  it  contains  nitrogen,  and  like  them  gives  off  some 
energy  when  oxidized,  but  it  is  not  a  true  proteid,  for  it  cannot  be  used 
in  the  building  of  body  tissues.  Substances  like  gelatine  are  called 
albuminoids,  meaning,  "like  the  albumins." 

Carbohydrates  include  the  starches  and  sugars . 
Starches  come  from  corn,  wheat,  potatoes,  and  other 
plants;  sugars  come  from  sugar  cane,  sugar  beets,  honey, 
fruits,  etc..  Carbohydrates  contain  carbon,  hydrogen, 
and  oxygen  only  (cf.  §  123) ;  no  nitrogen.  They  are  used 
by  the  body  for  the  energy  (heat)  that  they  furnish.  The 
body  seems  to  be  unable  to  use  starch  and  cane  sugar 
directly.  Starch  must  first  be  changed  to  maltose  (malt 
sugar),  and  this  to  dextrose  (also  called  glucose,  or  " grape 
sugar")-  Cane  sugar  must  be  changed  to  dextrose  and 
levulose  (fruit  sugar). 

Fats  and  oils  contain  carbon,  hydrogen,  and  oxygen, 
just  as  carbohydrates  do  (cf.  §  224).  They  are  present  in 
such  food  materials  as  milk,  butter,  lard,  olive  oil,  and  the 
fat  of  meat,  as  well  as  in  eggs,  corn,  peanuts,  etc.  Fats 
and  oils,  like  carbohydrates,  furnish  heat  and  energy  to 
the  body,  but  cannot  build  up  protoplasm.  The  student 
will  see  at  once  that  we  get  these  three  nutrients  (proteids, 
carbohydrates,  and  fats)  by  eating  the  bodies  or  products 
of  animals  and  plants. 

Our  chief  mineral  food  is  salt;  this  is  needed  for  important  digestive 
processes  (cf.  §  364).  Salt  is  present  in  many  foods,  and  is  used  to 


350  THE  HUMAN  BODY  AND  ITS  FOOD 

season  food.  Iron  compounds  are  needed  to  form  a  part  of  the  blood; 
we  get  them  chiefly  from  vegetable  food.  Limestone  and  calcium 
phosphate  are  needed  by  the  bones  (cf.  §  352).  We  get  them  in  our 
food  and  in  hard  water  (cf.  §  132). 

Water  is  needed  in  large  amounts  by  the  body.  We  realize  this 
when  we  remember  that  about  70%  of  the  body  is  water.  We  get  a 
great  deal  of  water  even  in  our  " solid"  food  (cf.  §  79). 

Oxygen  is  not  usually  thought  of  as  a  food,  because  it  does  not 
enter  the  body  by  the  digestive  organs;  but  the  body  must  have  an 
abundant  supply  of  it  all  the  time  to  remain  alive. 

358.  Organs  of  Digestion;  Glands. —  The  tube  through 
which  food  is  passed  for  digestion  is  called  the  alimentary 
canal,  or  digestive  tract.  It  consists  of  the  mouth, 
pharynx  (throat),  esophagus  (gullet),  stomach,  and  the 
large  and  small  intestines.  Altogether  it  is  about  30  feet 
long. 

In  order  to  digest  food,  liquids  are  poured  upon  it  in 
the  mouth,  the  stomach,  and  the  intestines.  The  liquids 
are  taken  out  of  the  blood  for  this  purpose  by  organs 
called  glands.  The  origin  of  glands  is  as  follows: 

The  alimentary  canal,  as  well  as  the  windpipe  and 
lungs,  is  lined  with  mucous  membrane.  This  begins  at 
the  lips,  and  is  a  continuation  of  the  skin  which  covers  the 
outside  of  the  body.  It  is  pink  from  the  network  of  blood 
vessels  beneath  it,  and  produces  a  thin,  clear  liquid  called 
mucus.  From  this  liquid  it  gets  its  name.  The  surface 
of  the  mucous  membrane  is  made  up  of  a  layer  of  flat  cells, 
called  epithelial  cells.  Now,  glands  are  made  by  the 
folding  in  of  epithelial  cells  in  tubes  or  pockets  (Fig.  278). 
Blood  vessels 'and  vessels  containing  lymph,  a  substance 
much  like  blood  (cf.  §  379),  are  all  about  the  glands;  hence 
it  is  only  necessary  for  the  epithelial  cells  to  take  what 


THE  MOUTH 


351 


material  they  want  from  the  blood.  They  then  give  off 
this  material  to  the  gland  pockets,  and  from  the  pockets 
it  is  poured  out  into  the  organ  for  which  it  was  intended. 
A  gland  separating  a  liquid  from  the  blood  is  said  to 
secrete  the  liquid,  and  the  liquid  is  called  a  secretion. 
The  glands  that  secrete  the  digestive  juice  of  the  mouth 
are  called  salivary  glands,  and  the 
secretion  is  saliva.  The  gastric 
glands  secrete  gastric  juice  for  the 
stomach. 


FIG.  278. 

Diagram  of  a  Simple  and  a 
Complex  Gland. 

During  chewing, 


359.  The  Mouth.— At  the  begin- 
ning of  the  digestive  tract  is  the 
mouth.  It  contains  the  nerves  of 
taste,  while  just  above  it,  in  the  nose, 
are  the  nerves  of  smell.  These  two 
senses  therefore  pass  upon  the  quality 
of  the  food  at  once.  In  the  mouth 
the  food  is  broken  up  into  bits 
(chewed,  or  masticated)  by  the  teeth, 
the  glands  of  the  mouth  secrete  saliva;  the  mouth 
1 '  waters."  They  often  secrete  it  before  food  gets  into  the 
mouth;  the  odor  or  thought  of  food  is  enough  to  put  them 
into  action.  The  tongue  rolls  the  food  about  in  the 
mouth,  so  that  the  teeth  may  chew  it  again  and  again. 
Finally,  when  we  wish  to  swallow  the  food,  the  tongue 
pushes  it  back  to  the  opening  of  the  throat,  or  pharynx. 

Saliva  consists  chiefly  of  water;  this  moistens  the  food 
thoroughly  before  swallowing  takes  place.  Some  of  the 
solution  of  the  food  also  gets  to  the  nerves  of  taste.  The 
saliva  is,  however,  more  than  water:  it  has  an  alkaline 


352 


THE  HUMAN  BODY  AND  ITS  FOOD 


reaction  (cf.  §  218) ;  it  contains  certain  salts,  also  ptyalin 
(pronounced  ti'-a-lin) ,  a  ferment,  or  enzyme. 

Ferments  are  substances  that  by  their  presence  bring 
about  chemical  changes  (cf.  §  98). 

Ptyalin  begins  the  change  of  starch  into  sugar  (cf.  §  357) ;  hence  a. 
cracker  becomes  sweet  when  chewed.  There  are  three  pairs  of  salivary 
glands  in  the  mouth:  one  pair  just  under  the  tongue;  another  behind 
the  corners  of  the  lower  jaws;  a  third  pair  in  front  of  the  ears. 

The  tongue  is  a  flat,  movable  organ  made  up  of  muscular  tissue. 
The  back  of  it  is  attached  to  the  bottom  of  the  mouth.  It  has  nerves 
of  touch,  like  those  of  the  finger  tips,  and  also  nerves  of  taste. 

The  cheeks  and  lips  are 
made  up  of  thin  muscles 
covered  with  skin  on  the  out- 
side and  with  mucous  mem- 
brane on  the  inside. 

360.  The  Teeth.— The 
adult  man  or  woman 
has  32  teeth,  set  into 
sockets  in  the  jaw  bones 
(Fig.  279).  The  teeth 
are  of  4  kinds,  called 

incisors,  canines,  bicuspids,  and  molars.  There  are  2 
incisors  ("cutters")  in  each  half  of  each  jaw.  They 
are  flat,  sharp  teeth  used  for  biting  off  pieces  of  food. 
Next  to  the  incisors  is  the  canine,  or  "dog,"  tooth. 
This  is  sharper  than  the  other  teeth.  In  the  dog  and 
other  carnivorous  animals  it  forms  the  tusk,  or  tearing 
tooth.  The  fourth  and  fifth  teeth  are  the  bicuspids,  so 
called  because  each  has  2  cusps,  or  points.  The  sixth, 
seventh,  and  eighth  teeth  are  the  molars,  or  grinding  teeth. 


Molars  Bicuspids 

FIG.  279. 
Teeth  in  the  Lower  Jaw. 


THE  SWALLOWING  OF  FOOD 


353 


The  child's  first  set  of  teeth  ("milk  teeth")  is  temporary.     There 
are  20  in  the  set.     When  the  child  is  6  or  7  years  old,  the  first  permanent 
teeth  appear.     These  are  the  first  of  the  permanent  molars.     The 
molars  farthest  back  in  each  jaw 
are  "cut"  last,  and  are  called  the 
"wisdom  teeth." 

A  tooth  consists  of  a  crown  of 
very  hard  enamel,  and  a  neck  and 
root  of  material  called  dentine.  The 
roots  are  covered  with  "  cement." 
The  interior  of  the  tooth  is  called 
the  pulp  cavity;  it  contains  the 
nerves  and  blood  vessels  of  the 
tooth.  The  teeth  are  precious, 
and  ought  to  be  given  every  care. 
They  should  be  cleaned,  every  day, 
with  a  soft  brush,  and  if  cavities 
are  formed  they  should  be  filled 
by  a  good  dentist.  Hard  sub- 
stances, such  as  nuts,  thread,  and 
brittle  candy,  should  not  be  bitten; 
for  they  may  break  the  enamel. 
If  bacteria  get  into  the  interior  of 
the  teeth,  they  cause  a  rapid  decay. 


361.  The  Swallowing  of 
Food. — When  food  is  ready 
to  be  swallowed,  the  tongue 
pushes  it  back  to  the  pharynx 
(Fig.  280).  This  is  a  mus-  FiG.2so. 

cular  tube,  about  4  inches     Pat^Take|^rFt0h°edBodybyAirasThey 
long,   having    a   number   of 

openings.     At   its   top  there  are   2   openings  into  the 
nose,  and  2  into  the  ears.     The   openings    leading   to 


354  THE  HUMAN  BODY  AND  ITS  FOOD 

the  nose  can  be  closed  by  the  soft  palate,  which  rises 
up  against  them.  The  opening  between  the  pharynx 
and  the  mouth  can  be  closed  by  two  upright  muscles, 
which  come  together  like  the  halves  of  a  sliding  door.  In 
passing  from  the  pharynx,  food  must  go  over  the  ' l  wind- 
pipe," or  trachea.  We  should  soon  be  strangled  if  food 
went  into  our  windpipes;  hence  the  larynx,  at  the  top  of 
the  windpipe,  is  closed  by  a  cover,  called  the  epiglottis. 
When  the  food  is  in  the  pharynx,  and  the  openings  to 
the  nose,  mouth,  and  windpipe  are  closed,  the  upper 
muscles  of  the  pharynx  contract  above  the  food,  forcing 
it  downward  into  the  esophagus.  This  is  a  tube  about  9 
inches  long,  lined  with  mucous  membrane,  and  provided 
with  circular  and  with  lengthwise  muscles.  The  esopha- 
gus muscles  contract  above  the  food,  and  force  it  down 
into  the  stomach. 

362.  Exercises. 

1.  What  advantages  has  the  internal  skeleton  of  vertebrates  over 
the  hard  external  covering  of  insects  and  crustaceans?     Has  it  any 
disadvantages? 

2.  What  advantages  does  man  gain  from  his  erect  position? 

3.  Name  several  levers  in  the  body. 

4.  How  could  you  find  out  how  much  of  the  weight  of  a  bone  is  due 
to  mineral  matter? 

5.  What  devices  are  there  in  the  skeleton  to  prevent  the  jarring  of 
the  softer  parts  of  the  body? 

6.  What  kind  of  a  joint  do  you  think  there  is  in  your  neck  that 
makes  it  possible  for  you  to  shake  your  head?    To  nod  "yes." 

7.  What  is  the  effect  of  high  heels  upon  the  position  of  the  body  in 
walking? 

8.  What  kind  of  a  joint  do  the  fingers  have?    What  kinds  has  the 
thumb?    What  are  the  structures  in  the  hand  that  make  it  so  skillful? 


THE  STOMACH  355 

9.  Why  does  your  head  nod  when  you  doze  in  your  chair? 

10.  Do  you  think  you  are  taller  at  night,  or  in  the  morning?    Meas- 
ure yourself,  and  explain  what  you  find  out. 

1 1 .  Give  the  reasons  why  sleep  rests  the  body. 

12.  We  are  told  that  milk,  and  cereals  such  as  oatmeal,  are  good  for 
young  children,  because  they  assist  in  bone  making.     What  nutrients 
must  they  supply? 

13.  Why  do  stones,  sand,  glass,  etc.,  have  no  taste? 

14.  Why  is  the  tongue  provided  with  nerves  of  touch? 

15.  Why  should  a  child's  first  teeth  be  cared  for,  even  though  they 
are  soon  to  be  replaced  by  the  permanent  set?    Why  ought  we  to  be 
careful  about  bringing  cold  food,  such  as  iced  water,  ice  cream,  and 
cold  melons,  in  contact  with  the  teeth? 

16.  Why  is  milk  called  a  " perfect"  food? 

17.  Yeast  contains  the  ferment  invertase,   which  changes  cane 
sugar  into  grape  sugar  and  fruit  sugar  (cf,  §  357).     It  also  contains 
zymase.    How  does  this  change  the  grape  and  fruit  sugars?     (Cf. 
§  129.) 

363.  The  Stomach. —  As  we  learned  in  §  361,  the 
esophagus  lies  against  the  backbone,  and  passes  through 
the  thorax  into  the  abdomen.  The  stomach,  at  the 
lower  end  of  the  esophagus,  is  wholly  within  the  abdomen, 
on  the  left  side,  and  partly  under  the  ribs.  It  is  about 
a  foot  long  and  about  4  inches  in  diameter.  The  stomach 
is  really  an  expansion  of  the  digestive  tract,  like  a  lake 
formed  by  the  widening  of  a  river.  There  is  nothing  to 
close  the  entrance  from  the  esophagus  into  the  stomach, 
but  the  opening  (pylorus)  from  the  stomach  into  the  small 
intestine  is  closed  by  a  muscular  ring  while  digestion  is 
going  on  in  the  stomach. 

The  method  by  which  food  is  carried  down  the  esopha- 
gus has  been  partly  explained  in  §  361:  the  circular 
muscles  contract  above  the  food.  The  esophagus  is  also 


356 


THE  HUMAN  BODY  AND  ITS  FOOD 


FIG.  281. 
Two  Kinds  of  Muscles. 


provided  with  lengthwise  muscles  (Fig.  281).  As  these 
can  be  shortened  by  contraction,  the  esophagus  can  carry 
out  movements  similar  to  those  described  for  the  earth- 
worm (cf.  §  336).  The  lengthwise  muscles  shorten  the 
tube,  and  pull  it  over  the  food,  while  the  circular  muscles, 

by  contracting,  form  a 
ring  behind  the  food,  and 
push  it  along. 

The  stomach  has  both 
of  these  kinds  of  muscles, 
and  in  addition  it  has 
oblique  muscles.  As  a 
result  of  the  action  of 
these  three  kinds  of 
muscles,  the  food  re- 
ceived from  the  esopha- 
gus is  forced  around  and  around  in  the  stomach.  It  is 
thus  mixed  thoroughly  with  the  gastric  juice,  the 
secretion  of  the  glands  of  the  stomach. 

364.  The  Gastric  Juice. — The  gastric  juice  is  chiefly 
water,  but  it  contains  the  important  ferments  rennin  and 
pepsin,  and  also  hydrochloric  acid,  in  solution.  From  5 
to  10  pints  are  secreted  daily.  Rennin  coagulates  the 
casein  (a  proteid;  §  357)  of  milk,  forming  "clots"  like 
those  of  sour  milk.  The  proteids  are  insoluble  in  water, 
and  cannot  pass  from  the  alimentary  canal  into  the  blood ; 
but  the  pepsin  changes  them  into  simpler  substances, 
called  peptones  and  proteoses,  which  are  soluble. 

The  hydrochloric  acid  of  the  stomach  (cf.  §  214)  carries  out  several 
important  reactions.  Thus,  pepsin  acts  best  when  hydrochloric 


THE  INTESTINES  357 

acid  is  present.  Again,  the  food  coming  to  the  stomach  is  alkaline, 
from  the  saliva  it  contains;  the  acid  neutralizes  this  (cf.  §  220).  Since 
food  is  exposed  to  the  air  before  we  eat  it,  it  contains  a  multitude  of 
bacteria,  including  those  of  fermentation.  The  acid  destroys  these, 
and  thus  prevents  fermentation  and  infection.  We  must  not,  however, 
depend  upon  the  hydrochloric  acid  to  destroy  all  bacteria,  for  some, 
such  as  those  of  typhoid,  are  not  killed  by  it. 

The  action  of  the  gastric  juice  changes  food  to  a  milky  substance 
called  chyme;  this  is  ready  for  digestion  in  the  intestines. 


365.  The  Intestines. — As  portions  of  food  are  changed 
to  chyme,  the  muscular  ring  at  the  pylorus  is  relaxed,  and 
the  chyme  enters  the  small  intestine.  Both  the  intestines 
together  form  a  tube  about  27  or  28  feet  long.  This  tube 
is  so  long  that  it  must  be  coiled  in  the  abdomen  (cf. 
Fig.  273,  §  350) .  Herbivorous  animals  have  even  longer  in- 
testines; that  of  the  grown  ox  is  about  150  feet  long  (cf. 
§  345).  In  man  the  small  intestine  is  about  22  feet  long 
and  1  inch  in  diameter;  the  large  intestine  is  about  2 
inches  in  diameter.  Both  of  these  have  lengthwise  and 
circular  muscles,  like  those  of  the  esophagus. 

Three  glands  discharge  their  secretions  into  the  small 
intestine;  the  glands  are  the  intestinal  glands  (which 
secrete  the  intestinal  juice),  the  liver,  and  the  pancreas. 
All  of  these  secretions  have  an  alkaline  reaction,  and  thus 
differ  from  the  gastric  juice,  which  has  an  acid  reaction. 

The  organs  that  are  of  the  greatest  importance  in 
absorbing  the  digested  food  of  the  small  intestine,  and  in 
transferring  nutriment  from  the  alimentary  canal  to  the 
blood,  are  the  villi  (singular,  villus).  These  .are  small 
elevations  that  project  from  the  wall  of  the  small  intestine, 
and  make  its  absorbing  surface  about  6  or  7  times  as 


358  THE  HUMAN  BODY  AND  ITS  FOOD 

great  as  if  it  were  smooth.  Each  villus  contains  a  net- 
work of  small  blood  tubes  (capillaries),  and  also  lacteal 
glands.  The  "food  solution,"  called  chyle,  which  the 
small  intestine  prepares,  goes  into  the  epithelial  cells  of 
the  villi,  and  from  these  cells  the  blood  tubes  and  lacteals 
absorb  it.  The  lacteal  glands  absorb  the  digested  fats; 
the  blood  tubes  absorb  the  other  kinds  of  food. 

Between  the  small  intestine  and  the  large  one  there  is  a  narrow 
opening  which  allows  food  to  pass.  The  large  intestine  begins  at  the 
level  of  the  right  hip,  passes  up  the  right  side  to  the  diaphragm,  then 
across  the  abdomen  to  the  left  side,  and  down  the  left  side.  It  does 
some  of  the  work  of  absorption,  although  it  has  no  villi;  but  its  chief 
use  is  to  discharge  the  solid  waste  from  the  body.  It  takes  about  2 
days,  under  normal  conditions,  for  food  to  pass  the  length  of  both 
intestines. 

The  vermiform  appendix,  which  when  inflamed  produces  appendi- 
citis, is  in  the  large  intestine,  near  the  place  where  the  small  intestine 
and  large  intestine  unite.  It  is  a  small,  closed  tube,  about  %  of  an 
inch  in  diameter,  and  about  2  inches  long. 

366.  The  Liver. — The  liver  is  a  dark-red  organ  weigh- 
ing about  4  pounds  (Fig.  282).  It  is  on  the  right  side  of 
the  abdomen,  under  the  lower  ribs  (see  also  Fig.  273, 
§  350).  The  liver  has  several  very  important  functions. 
For  one  thing,  it  helps  to  remove  from  the  blood  the  waste 
nitrogen  compounds  formed  by  the  destruction  of  the 
cells.  A  second  function  of  the  liver  is  to  make  and 
to  store  glycogen,  a  starchlike  substance  that  is  readily 
changed  to  sugar  when  the  body  needs  it.  A  third  use 
of  the  liver  is  to  secrete  bile,  a  yellow,  bitter  liquid,  which 
is  emptied  by  the  bile  tube  into  the  small  intestine. 

The  bile  is  collected  from  the  blood  by  a  multitude  of  bile  ducts.  A 
tube  leads  from  the  liver  to  the  gall  bladder,  a  sac  that  receives  and 


THE  PANCREAS 


359 


stores  the  bile  when  it  is  not  needed.  When  the  pylorus  allows  food  to 
pass  from  the  stomach  into  the  small  intestine,  the  bile  is  poured  out 
for  the  food's  digestion. 

The  bile  lubricates  the  intestine,  and  helps  all  the  operations  of 
digestion  and  absorption  in  the  intestine.     When  bile  is  not  secreted 


Adjace 
Lobules 


Fig.  282. 
Diagram  Showing  the  Structure  of  the  Liver. 


properly,  biliousness,  accompanied  by  headache  and  indigestion,  is 
the  result. 


367.  The  Pancreas. — We  have  already  learned  about 
some  of  the  ferments  of  the  digestive  tract:  the  ptyalin 
of  the  saliva  (cf.  §  359)  and  the  rennin  and  pepsin  of  the 
gastric  juice  (cf.  §  364).  Important  as  these  ferments  are, 
they  are  not  so  important  as  the  ferments  that  are  poured 
into  the  small  intestine  in  the  secretion  known  as  the 


360  THE  HUMAN  BODY  AND  ITS  FOOD 

pancreatic  juice.     The  ferments  of  the  pancreatic  juice 
are— 

(1)  Amylopsin,  which  completes  the  digestion  of  starchy 
foods  ("amylum"  means  starch). 

(2)  Steapsin,  which  digests  fats  ("stear"  means  fat). 

(3)  Trypsin,  which  completes  the  digestion  of  proteids 
(its   name   means    "  something   that    '  wears   down/    or 
digests"). 

The  pancreatic  juice  is  a  thin,  watery  liquid,  like  saliva.  The 
pancreas,  which  secretes  it,  is  a  tongue-shaped  gland  about  6  inches 
long  and  one  inch  in  diameter.  It  lies  behind  the  stomach  (see- 
Fig.  273,  §  350).  The  pancreas  of  the  lower  animals,  such  as  the  pig,  is 
called  sweetbread.  The  duct  from  the  pancreas  unites  with  that 
from  the  liver,  so  both  the  bile  and  the  pancreatic  juice  enter  the 
small  intestine  through  the  same  opening. 

368.  Changes  in  Food  by  Digestion. — Let  us  now  look  at 
the  process  of  digestion  as  a  whole,  and  ask :  ' '  What  is  the 
fundamental  thing  that  digestion  in  the  mouth,  stomach, 
and  intestines  does?"  The  answer  is  that  this  digestion 
makes  food  soluble,  so  that  it  can  go  through  the  wall  of 
the  alimentary  canal  into  the  blood  and  lymph.  Most  of 
the  proteids  do  not  dissolve  in  water;  neither  do  the  fats 
and  starch.  Why  do  they  not  dissolve?  We  have  already 
learned  that  scientists  believe  that  matter  consists  of 
small  particles  called  molecules  (cf.  §  61).  Now,  chemists 
believe  that  a  part,  at  least,  of  the  reason  why  proteids, 
fats,  and  starch  do  not  dissolve  is  that  their  molecules 
are  too  large,  and  therefore  too  inactive.  To  make 
these  food  materials  dissolve,  their  molecules  must  be 
broken  down  into  smaller  molecules.  This  is  the  work 
that  the  ferments,  or  enzymes,  perform  in  digestion. 


ABSORPTION,  ASSIMILATION,  AND  STORAGE  OF  FOOD      361 

We  have  already  had  illustrations  of  the  action  of  these 
ferments.  Thus,  the  amylopsin  of  the  pancreatic  juice 
changes  the  large  molecules  of  starch  to  the  smaller 
molecules  of  malt  sugar.  In  this  form  it  is  soluble.  But 
even  the  malt  sugar  molecule  must  later  be  broken  up 
into  dextrose  molecules  for  the  use  of  the  cells.  Out  of 
the  malt  sugar  molecule  the  ferment  maltase  produces 
two  dextrose  molecules.  The  ptyalin  of  the  saliva  begins 
the  change  of  starch  into  sugar,  but  does  not  finish  it. 
The  pepsin  of  the  stomach,  acting  under  acid  conditions, 
breaks  up  some  of  the  complex  proteid  molecules  into 
peptones,  which  are  soluble  in  the  gastric  juice.  Proteid 
digestion  is  not,  however,  completed  in  the  stomach,  so 
the  trypsin  of  the  pancreatic  juice,  acting  under  alkaline 
conditions,  completes  the  process.  In  some  similar  way 
the  steapsin  of  the  pancreatic  juice  changes  the  fats  into 
soluble  form.  It  probably  does  this  by  decomposing  the 
fats  into  glycerine  and  acids.  The  acids  formed  are  the 
11  fatty  acids"  (cf.  §  224),  such  as  stearic  acid,  oleic  acid, 
etc.  Butter  would  give  chiefly  butyric  acid  (from  butyrum, 
"butter").  Of  these  fatty  acids  butyric  acid  is  the  only 
one  that  is  very  soluble,  in  the  strict  sense  of  the  word. 
But  the  other  acids  are  broken  up,  in  the  small  intestine, 
into  very  minute  particles,  so  that  they  form  a  part  of  an 
emulsion,  like  milk  (cf.  §  91) .  This  emulsion  can  be  taken 
through  the  cell  walls  of  the  villi,  and  into  the  lacteal 
glands  (cf.  §  365). 

369.  Absorption,  Assimilation,  and  Storage  of  Food. — 

Absorption   (cf.   §  365)  is  not  only  the  transferring  of 
digested  food  to  the  blood;  strangely  enough,  the  peptones, 


362  THE  HUMAN  BODY  AND  ITS  FOOD 

fatty  acids,  glycerine,  maltose,  etc.,  which  are  formed  by 
digestion,  are  not  found  in  the  blood.  The  blood  does 
contain  fats,  formed  out  of  the  glycerine  and  the  fatty 
acids ;  proteids,  formed  out  of  the  peptones  and  proteoses ; 
and  grape  sugar,  formed  out  of  the  maltose.  From  this  it 
may  seem  that  absorption,  so  far  as  the  fats  and  proteids 
are  concerned,  undoes  the  work  of  the  other  stages  of 
digestion.  But  we  must  remember  that  the  complex 
molecules  of  our  food  are  not  the  actual  nutrients  that  the 
cells  can  use,  although  they  contain  the  "pieces"  (small 
molecules)  out  of  which  the  body's  fats  and  proteids  can  be 
constructed.  Digestion  must  be  looked  upon  not  simply 
as  a  breaking  down  of  large  molecules,  but  also  as  a 
recombining  of  the  small  molecules  of  digested  food  to 
form  the  special  fats  and  proteids  of  the  body. 

The  last  stage  in  the  digestive  process  is  called  assimila- 
tion, which  means  "making  similar  to."  Assimilation 
takes  place  at  the  cells.  Here  the  proteid  brought  by  the 
blood  and  lymph  becomes  a  part  of  the  living  protoplasm. 
Here  also,  in  some  mysterious  way,  the  cell  protoplasm 
causes  the  sugar  and  fat,  and,  to  some  extent,  the  pro- 
teids, to  unite  with  oxygen  (cf.  §  52).  It  is  this  chemical 
reaction  that  sets  free  the  energy  which  the  cells  must 
have  to  do  their  work,  and  which  keeps  the  body  warm. 

Storage  of  Food. — We  eat  only  at  intervals,  while  the  body  needs 
food  all  the  time.  Hence  there  must  be  ways  in  which  food  can  b3 
stored  up  during  the  time  of  abundance,  in  order  that  the  body  may 
have  a  supply  to  draw  upon  when  its  cells  wear  out,  and  its  energy  is 
low.  We  have  already  learned  that  carbohydrates  are  stored  up  by 
the  liver  (cf.  §  366)  as  glycogen.  The  muscles  also  store  glycogen. 
When  dextrose  is  taken  from  the  blood,  by  the  cells,  glycogen  is 
changed  to  sugar  to  keep  up  the  blood's  supply. 


OUR  DIET  363 

Fat  is  stored  away  in  the  spaces  of  connective  tissue,  as  under  the 
skin  (cf.  Fig.  291,  §  392),  between  the  muscles,  and  among  the  organs 
of  the  abdomen.  Fat  so  stored  forms  fat  tissue.  Animals  that  are 
inactive  in  winter  (hibernate ;  cf.  §  342)  usually  store  up  a  large  amount 
of  fat  to  nourish  their  bodies  during  their  long  fasting.  The  blubber 
of  the  whale  is  a  thick  layer  of  fat  stored  under  the  skin.  The  camel's 
hump  is  fatty  material  that  can  be  drawn  upon  when  the  animal  has  no 
opportunity  for  feeding. 

370.  Our  Diet. — Does  it  make  any  difference  what  kind 
of  coal  we  burn  under  a  steam  boiler?  If  you  were  to  ask 
a  wide-awake  engineer  such  a  question,  he  would  prob- 
ably answer  (cf.  §  73) :  ' '  Certainly  it  does.  Some  coals 
give  more  heat  than  others.  Some  coals  leave  great 
quantities  of  clinkers,  while  others  burn  up  clean.  And 
the  most  expensive  coal  is  not  always  the  best."  So  it  is 
with  the  fuel  of  the  body,  our  food.  It  makes  a  great 
deal  of  difference  what  kind  of  food  we  eat,  how  it  is 
cooked  and  served,  and  what  it.  costs.  We  need  to  eat 
some  food  for  the  energy  it  will  give  us,  and  some  for  its 
power  of  building  the  worn-out  tissues.  Some  apparently 
good  food  is  mostly  waste,  like  the  clinkery  coal ;  and  some 
food,  though  expensive  to  buy,  has  not  a  high  nutritive 
value. 

The  study  of  diet  forms  a  science  by  itself;  it  is  called 
dietetics.  Its  experts  are  very  careful  to  plan  what  they 
call  a  "balanced  ration,"  and  a  housekeeper  should  be 
equally  particular.  A  meal  should  not  consist  all  of  one 
kind  of  nutrients,  or  some  of  the  digestive  organs,  or  their 
ferments,  will  be  overtaxed  with  work,  while  others  will 
have  nothing  to  do.  The  housekeeper  has  a  great 
responsibility,  not  only  for  the  health  of  the  persons  fed, 


364  THE  HUMAN  BODY  AND  ITS  FOOD 

but  also  for  their  efficiency  in  their  work;  that  is,  for  what 
they  do  as  compared  with  what  they  could  do. 

A  grown  man,  weighing  about  154  pounds,  and  doing  a  moderate 
amount  of  muscular  work,  needs  from  60  to  115  grams  (3  to  5  ounces) 
of  proteids  per  day.  Part  of  these  may  be  vegetable  proteids.  In 
addition,  he  needs  enough  fats  and  carbohydrates  to  give  him  energy  to 
the  amount  of  3,000  or  3,400  large  calories.  A  large  calorie  is  1,000 
ordinary  calories  (c/.  §  64).  This  is  about  the  amount  of  heat  pro- 
duced by  the  burning  of  1  pound  of  carbon.  We  commonly  get  our 
energy  from  cereals,  bread,  potatoes,  sugar,  fat,  etc. 

There  is  a  great  difference  in  the  price  of  foods,  when  they  are 
considered  as  energy-producers.  If  corn  costs  !}/£  cents  a  pound,  1 
cent's  worth  of  corn  will  give  off  1,200  calories  of  heat,  while  1  cent's 
worth  of  codfish  will  give  off  only  20  calories,  and  1  cent's  worth  of 
oysters  only  12  calories.  Unless  a  family  is  careful,  it  may  pay  high 
prices  for  food,  and  yet  not  be  as  well  nourished  as  a  family  with  a 
simple  and  inexpensive,  but  well  selected  diet. 

But  we  must  remember  that  fresh  vegetables,  which  give  us  almost 
no  proteid  and  fat,  and  but  little  carbohydrate,  are  very  important 
for  the  mineral  salts  they  contain,  and  because  they  give  bulk  to  our 
food.  We  cannot  estimate  the  value  of  a  food  in  terms  of  proteids  and 
energy  alone. 

Whether  food  is  cheap  or  expensive,  it  should  be  made 
appetizing  and  nutritious  by  proper  cooking  and  serving. 
Cooking  does  not  add  to  the  nutrients  of  the  food,  but  it 
adds  greatly  to  the  digestibility.  It  softens  and  loosens 
the  tissues  of  food,  and  enables  the  digestive  juices  to  get 
at  them.  Proper  cooking  kills  the  parasites,  such  as 
bacteria,  that  cling  to  food,  and  the  trichinae  (small 
worms)  and  young  tapeworms  that  are  sometimes  found 
in  raw  meat.  Meat  is  especially  likely  to  be  improperly 
cooked.  If  it  is  fried  or  roasted,  it  should  be  seared  on 
the  outside  by  being  heated  very  hot  at  once;  in  this  way 


ALCOHOL  AND  ITS  EFFECTS  365 

the  nutritive  juices  are  held  inside.  Overdone  meat  has 
lost  much  of  its  value.  Much  frying  in  fat,  of  such  food 
as  eggs,  meat,  and  potatoes,  is  not  good,  for  it  covers  the 
food  with  a  greasy  coating,  which  the  digestive  juices  of 
the  mouth  and  stomach  cannot  penetrate. 

Here  are  some  of  the  foolish  things  people  do;  then  they  wonder  why 
they  have  indigestion : — 

(1)  They  do  not  take  enough  exercise,  yet  they  eat  large  amounts  of 
food. 

(2)  They  do  not  eat  enough  food  of  the  plain  sort,  but  eat  too  much 
of  pickles,  candies,  cake,  and  pie. 

(3)  They  take  violent  exercise  too  near  meal  time.     If  this  comes 
just  before  the  meal,  the  body  is  too  tired  to  digest  food  properly;  if 
after  the  meal,  the  body  has  not  time  to  digest  food  before  its  energy 
is  needed  for  other  purposes. 

(4)  They  eat  frequently  between  meals,  never  giving  the  stomach  a 
rest.     If  one  is  exercising  hard,  however,  especially  if  he  has  not  eaten 
the  slowly  digestible  food  that  " stays  by,"  a  "bite"  between  meals  is 
helpful. 

5.  People  often  drink  very  cold  ("iced")  water,  and  so  chill  the 
stomach. 

6.  They  do  not  eat  slowly  enough,  so  that  the  food  is  not  mixed  with 
the  saliva. 

371.  Alcohol  and  Its  Effects —  The  story  of  the  injury 
alcohol  has  done  to  men  is  a  long  and  sad  one,  but  at  pres- 
ent we  shall  consider  only  its  effect  upon  the  digestion  and 
assimilation  of  food,  and  its  injury  to  the  digestive  organs. 
When  alcohol  is  poured  over  proteids,  outside  of  the  body, 
it  makes  them  coagulate,  or  harden,  so  that  they  will  not 
decay  or  ferment.  This  is  a  good  thing  in  the  preserving 
of  animal  specimens,  but  it  is  not  what  we  want  in  the  case 
of  a  food.  For  food,  as  we  have  learned,  is  eaten,  not 


366  THE  HUMAN  BODY  AND  ITS  FOOD 

that  it  may  be  preserved,  but  that  it  may  be  broken  down 
by  the  ferments  of  the  body.  A  strong  drinker  suffers 
from  stomach  indigestion  largely  because  his  food  has 
been  hardened  and  made -unfit  for  the  body.  Besides 
injuring  the  food,  alcohol  paralyzes  the  stomach  muscles, 
so  that  they  cannot  mix  the  food  thoroughly  with  the 
gastric  juice. 

We  learn  that  the  using  up  of  proteids  at  the  cells  pro- 
duces body  wastes  (cf.  §§  366  and  380).  One  of  the  most 
important  of  these,  and  very  injurious  if  retained  in  the 
body,  is  uric  acid.  The  cells  pass  uric  acid  over  to  the 
lymph,  and  the  lymph  hands  it  over  to  the  blood.  The 
blood  carries  it  to  the  liver.  Now,  in  health,  the  liver 
changes  a  large  part  of  the  uric  acid  to  urea,  a  soluble 
solid  that  is  removed  from  the  body  by  the  kidneys.  But 
alcohol,  even  the  small  amount  in  a  glass  of  beer  or  wine, 
may  so  upset  the  liver  that  the  breaking  up  of  uric  acid 
into  urea  is  prevented,  and  the  waste  material  is  retained, 
greatly  to  the  injury  of  the  body. 

Those  who  defend  the  using  of  alcohol  often  tell  us  that 
it  is  a  food.  It  is  true  that  a  small  amount  of  it  can  be 
oxidized  at  the  cells,  and  that  this  oxidation  gives  some 
energy ;  but  it  is  also  true  that  the  cells  are  greatly  injured 
by  it,  and  that  for  this  reason  it  cannot  properly  be  called 
a  food,  but  must  be  called  a  poison.  The  only  reason  for 
which  drinkers  insist  on  calling  alcohol  a  food  is  that  they 
want  an  excuse  for  satisfying  the  alcohol  appetite.  Alco- 
hol undergoes  no  process  of  digestion.  It  passes  at  once 
from  the  stomach  into  the  blood  and  the  lymph,  and  to 
the  cells.  But  there  is  too  much  alcohol  for  the  cells 
even  in  the  amount  taken  by  a  moderate  drinker.  Now, 


ALCOHOL  AND  ITS  EFFECTS 


367 


when  real  food  is  digested  in  an  amount  that  is  beyond 
what  the  cells  need,  it  can  be  stored.  In  this  way  sugar 
and  fat  are  stored  (cf.  §  369).  But  alcohol  cannot  be 
stored.  That  which  cannot  be  oxidized  at  once  becomes 
simply  waste,  carrying  harm  wherever  it  goes. 

Many  patent  medicines  contain  a  great  deal  of  alcohol 
(Fig.  283),  and  people  take  them  without  realizing  this 


3  to  6% 


Wine 
6  to  10% 


Some 
Patent 
Medicines 
15  to  26% 


A 


Scotch 
Whisky 
39% 


FIG.  283. 
Amounts  of  Alcohol  Present  in  Liquors  and  in  Some  Patent  Medicines. 


fact.  A  medicine  containing  alcohol  will  produce  all  the 
effects  of  alcoholic  liquors,  and  will  develop  an  alcohol 
appetite  in  persons  who  would  not  think  of  becoming 
drinkers.  Patent  medicines  may  also  contain  injurious 
drugs,  such  as  opium,  chloral,  etc.  An  illustration  is  the 
11  soothing  syrup"  that  is  often  given  to  young  children. 
People  ought  to  know  that  when  they  are  giving  a  ' '  pare- 
goric" soothing  syrup,  they  are  giving  a  preparation  of 
opium,  and  that  the  child  becomes  quiet,  not  because  it  is 
cured,  but  because  it  is  stupefied.  The  after-effects  of 


368  THE  HUMAN  BODY  AND  ITS  FOOD 

such  drugs  are  often  very  injurious.  No  medicine  of 
this  sort  should  be  taken  or  given  unless  a  competent 
physician  prescribes  it. 

372.  Summary. — Physiology  is  the  science  that  has  to  do  with  the 
organs  of  animals  and  plants,  and  with  the  functions  of  the  organs. 

Man  is  a  vertebrate.  His  body  has  a  dorsal  and  a  ventral  cavity. 
The  dorsal  cavity  contains  the  brain  and  spinal  cord.  The  ventral 
cavity  consists  of  the  thorax  and  abdomen.  These  are  divided  by  the 
diaphragm. 

The  body  is  composed  of  living  cells.  A  group  of  cells,  all  of  which 
do  the  same  kind  of  work,  is  called  a  tissue. 

Bones  are  made  chiefly  of  connective  tissue  stiffened  with  limestone 
and  calcium  phosphate.  Cartilage  is  pliable,  immature  bone. 

Joints  are  places  where  bones  come  together;  they  are  movable  or 
immovable. 

At  movable  joints  bones  are  held  together  by  ligaments.  Movable 
joints  may  be  hinge,  ball  and  socket,  or  gliding  joints. 

The  skeleton  consists  of  206  bones. 

Muscles  are  structures  that  move  the  body.  Their  duty  is  to  grow 
shorter.  Muscles  are  made  of  muscle  tissue  and  connective  tissue. 

Tendons  are  the  extensions  of  the  muscles'  connective  tissue. 

The  bones  act  as  levers,  muscles  being  the  "power." 

Muscles  are  voluntary  or  involuntary. 

When  bones  of  a  joint  are  separated,  the  joint  is  said  to  be  "dis- 
located." In  a  ' '  sprain  "  the  bones  remain  together,  but  the  ligaments 
are  injured. 

We  eat  food  (1)  to  provide  for  cell  growth  and  repair;  (2)  to  provide 
energy  for  the  cells. 

There  are  5  simple  foods,  or  nutrients:  proteids,  carbohydrates, 
fats,  minerals,  and  water.  Proteids  give  material  for  the  growth  and 
repair  of-  cells,  also  a  little  energy.  Carbohydrates  and  fats  give 
energy. 

The  tube  in  which  digestion  occurs  is  the  alimentary  canal,  or  diges- 
tive tract.  Digestion  is  carried  out  by  liquids  taken  from  the  blood 
(secreted)  by  organs  called  glands. 


SUMMARY  369 

The  mou^h.  contains  salivary  glands,  which  secrete  saliva.  Saliva 
contains  a  ferment,  ptyalin. 

Ferments,  or  enzymes,  are  substances  that  by  their  presence  bring 
about  chemical  changes. 

The  teeth  crush  the  food,  and  mix  it  with  the  saliva. 

Food  is  swallowed  by  the  action  of  the  muscles  of  the  tongue, 
pharynx  and  esophagus. 

Food  enters  the  stomach  from  the  esophagus,  and  leaves  it  at  the 
pylorus  opening,  entering  the  small  intestine. 

Gastric  juice  contains  the  ferments  rennin  and  pepsin,  and  hydro- 
chloric acid.  Pepsin  begins  the  digestion  of  proteids. 

Digestion  in  the  small  intestine  is  carried  out  by  the  secretions  of 
3  glands.  The  intestinal  glands  secrete  the  intestinal  juice.  The 
liver  secretes  the  bile.  The  pancreas  secretes  the  pancreatic  juice. 

The  pancreatic  juice  contains  the  ferments  amylopsin,  steapsin,  and 
trypsin;  these  complete  the  digestion  of  carbohydrates,  fats,  and  pro- 
teids, respectively.  Intestinal  digestion  takes  place  under  alkaline 
conditions. 

Absorption  in  the  small  intestine  takes  place  through  the  villi; 
these  contain  blood  tubes  and  lacteal  glands. 

The  object  of  digestion  is  (1)  to  get  the  food  into  soluble  form,  and 
(2)  to  get  the  large  molecules  of  food  substances  into  smaller  molecules 
that  can  recombine  to  form  the  molecules  actually  needed  by  the  cells. 

Assimilation  is  the  bringing  together  of.  food,  oxygen,  and 
the  cells. 

Food  is  stored  as  glycogen  (in  the  liver),  and  as  fat.  The  stomach 
acts  as  a  temporary  storage  organ. 

Dietetics  is  the  science  of  our  diet.  We  need  a  " balanced"  diet, 
containing  the  best  possible  proportions  of  cell-building  and  of  energy- 
producing  material. 

Good  cooking  and  good  serving  are  as  important  as  proper  kinds  of 
food. 

Indigestion  is  often  the  result  of  our  own  carelessness. 

Alcohol  coagulates  the  proteids,  and  makes  their  digestion  hard;  it 
therefore  brings  on  stomach  indigestion.  It  interferes  with  the  action 
of  the  liver,  so  that  body  wastes  are  left  in  the  blood. 


370  THE  HUMAN  BODY  AND  ITS  FOOD 

Alcohol  cannot  be  looked  upon  as  a  food,  for  it  has  the  effects  of  a 
poison. 

Many  patent  medicines  contain  alcohol,  and  are  as  dangerous  as 
alcoholic  liquors. 

373.  Exercises. 

1.  What  nutrient  in  milk  is  coagulated  when  milk  sours?    What 
stomach  ferment  clots  it?    What  is  a  "full  cream"  cheese?    What 
nutrients  does  it  contain?    What  ferment  is  there  in  the  dessert  called 
"  junket"? 

2.  What  are  the  chief  nutrients  in  bread,  meat,  sweet  potatoes, 
peanuts,  fruit? 

3.  Name  an  easily  digested  fatty  food. 

4.  Trace  the  course  of  meat  through  the  alimentary  canal  until  it 
reaches  the  cells,  naming  the  organs  it  passes  through,  and  the  change 
each  brings  about. 

5.  Cases  have  been  known  in  which  surgeons  have  removed  a  pa- 
tient's stomach,  and  attached  the  small  intestine  directly  to  the 
esophagus.     Could  a  person  without  a  stomach  digest  all  kinds  of 
food?    What  would  be  the  chief  disadvantage? 

6.  What  changes  occur  in  the  absorption  of  food? 

7.  Name  all  the  different  functions  of  the  liver  that  have  been  given 
in  this  chapter. 

8.  Show  that  the  energy  of  animal  bodies  comes,  finally,  from  the 
sun. 

9.  In  what  part  of  the  digestive  tract  are  fats  digested?    What 
ferment  is  lacking  if  the  body  cannot  digest  them  properly?    What 
ferments  are  lacking  if  potatoes  cannot  be  digested?    Meat? 

10.  What  sugars  does  the  body  derive  from  cane  sugar?    From 
malt  sugar? 

11.  Why  do  we  "raise"  bread?    How?    Why  is  bread  "heavy," 
or  "soggy"?    What  is  the  objection  to  our  eating  it?    How  is  cake 
raised?    How  is  ' l  angel  food  "  cake  raised? 

12.  Suggest  a  reason  why  "toasted"  bread  is  so  healthful.    Why 
are  baked  potatoes  healthful?    Why  is  a  soft-boiled  egg  more  digestible 
than  a  hard-boiled  one? 


EXERCISES  371 

13.  Why  does  soup  alone  not  make  a  full  dinner?    When  a  man 
doing  physical  labor  eats  too  large  a  proportion  of  meat,  he  becomes 
hungry  long  before  meal  time,  while  if  he  has  a  fair  share  of  vegetables 
and  bread,  his  meal  "  stays  by/'  as  he  says,  until  the  next  meal.     Ex- 
plain why. 

14.  Strychnine  contains  carbon,  hydrogen,  oxygen,  and  nitrogen; 
is  it  therefore  a  food?     Why  cannot  alcohol  be  properly  called  a  food? 

15.  Do  you  think  that  the  following  meal  is  "balanced,"  so  far  as 
proteids,  carbohydrates,  and  fats  are  concerned:  soup,  fried  potatoes, 
bread,  and  rice  pudding?     What  do  you  say  of  the  following  menu: 
ham  and  eggs,  potatoes,  nut  salad,  and  mince  pie?     How  about  this 
one:  steak,  baked  potatoes,  sliced  tomatoes,  and  baked  apples? 

16.  What  is  the  value  of  a  vegetable  salad  in  a  dinner? 

17.  Find,  in  a  newspaper  or  magazine,  a  menu  for  breakfast,  dinner, 
and  supper,  and  discuss  it  as  to  its  food  values  and  its  economy. 

18.  What  foods  are  omitted  from  an  athletic  training  table,  and 
why? 

19.  Why  can  a  dog  digest  bone?    Why  can  he  eat  decayed  meat, 
while  man  can  not?     (Cf.  §§  214  and  364.) 


CHAPTER  XVIII 

CIRCULATION  AND  RESPIRATION 

374.  The  Circulation  of  the  Blood. — Just  as  the  work 
of  Newton  is  the  foundation  of  modern  Physics,  and 
as  Lavoisier's  explanation  of  burning  was  the  beginning 
of  modern  Chemistry,  so  Harvey's  discovery  that  the 
blood  circulates  through  the  body  was  the  starting  point 
of  modern  Physiology.  Harvey,  an  English  physician, 
made  his  discovery  about  1616.  The  blood  has  several 
very  important  functions.  The  food  that  is  digested  in 
the  alimentary  canal  must  be  carried  to  the  individual 
cells  all  over  the  body  (cf.  §  369);  the  blood  carries  it. 
The  oxygen  that  is  taken  into  the  body  at  the  lungs  must 
also  be  taken  to  the  cells;  so  the  blood  has  the  power  of 
carrying  oxygen.  The  cells  in  the  exposed  parts  of  the 
body  (those  near  the  skin,  for  example)  must  be  kept 
warm,  so  that  the  protoplasm  can  continue  its  work; 
hence  the  blood  is  a  carrier  of  heat,  and  keeps  up  the 
body's  temperature.  The  reaction  between  the  food  and 
oxygen,  which  takes  place  at  the  cells,  gives  energy,  but 
it  also  produces  waste  materials  (cf.  §§  366  and  371). 
These  must  not  accumulate,  or  they  will  poison  the  body. 
Hence  the  blood  serves  as  the  great  sewer  into  which  the 
wastes  of  the  cells  are  discharged. 

A  system  carrying  liquids  through  the  body  needs  a 
pump,  or  heart.  The  other  organs  of  circulation  are  the 
arteries,  veins,  and  capillaries.  There  are  also  spaces 

372 


THE  HEART 


373 


between  the  blood  tubes  and  the  cells;  these  are  filled 
with  lymph,  a  liquid  much  like  the  blood  (cf.  §  379). 

375.  The  Heart.— The  heart  (Fig.  284)  lies  in  the  cavi- 
ty of  the  thorax,  almost  surrounded  by  the  lungs.  The 
smaller  end  is  to  the  left  of  the 
breast  bone,  but  the  larger  end 
is  directly  behind  it.  The  heart 
of  a  person  is  about  as  large  as 
his  fist.  The  heart  proper  is 
surrounded  by  a  protective  cov- 
ering with  a  double  wall.  This 
is  the  pericardium,  meaning 
"around  the  heart."  Between 
the  two  halves  of  the  pericar- 
dium there  is  a  liquid  that  de- 
creases the  friction  of  the  heart 
in  its  movements. 

The  heart  of  man,  like  that 
of  all  mammals  (cf.  §  345),  con- 
sists of  4  cavities,  or  chambers. 
These  chambers  are  all  needed,  because  the  blood  goes 
through  2  distinct  circuits,  or  "round  trips."  One  of 
these  circuits  is  from  the  heart  to  the  body,  and  then 
back  to  the  heart.  This  is  the  system,  or  body,  circula- 
tion. The  other  circuit  is  from  the  heart  to  the  lungs,  and 
back  again  to  the  heart.  This  is  the  lung,  or  pulmonary, 
circulation.  The  two  upper  cavities  of  the  heart  are  the 
right  auricle  and  the  left  auricle  (compare  again  the  heart 
of  the  crayfish,  fish,  frog,  and  bird) .  The  auricles  receive 
the  blood  from  the  body  and  lungs.  The  heart's  two 


Right  Ventric 


FIG.  284. 

The  Heart.  Veins  bring  blood  to 
the  auricles,  and  arteries  carry  it 
away  from  the  ventricles.  Note 
the  valves,  and  the  means  of  hold- 
ing them  shut. 


374  CIRCULATION  AND  RESPIRATION 

lower  chambers  are  the  right  and  left  ventricles.  The 
auricles  force  the  blood  into  the  ventricles;  then  the  ven- 
tricles exert  the  pressure  that  drives  the  blood  to  the 
body  and  lungs.  The  ventricles  have  much  thicker  walls 
than  the  auricles,  because  they  have  so  much  harder 
work  to  do;  and  the  left  ventricle,  which  forces  the 
blood  through  the  body  circulation,  has  walls  much 
thicker  than  the  right  ventricle,  which  sends  the  blood 
through  the  lungs. 

The  heart  has  4  valves  which  permit  its  outlets  to  be  opened  and 
closed.  The  valves  are  made  of  tough  connective  tissue,  and  are 
strengthened  by  cords  fastening  them  to  the  walls  of  the  heart.  Blood 
pressing  on  one  side  of  the  valves  makes  them  open,  but  when  the 
pressure  is  on  the  other  side,  they  come  together,  and  prevent  the 
blood  from  flowing  backward.  We  are  accustomed  to  think  of  the 
heart  as  a  pump;  we  must  rather  think  of  it  as  4  pumps.  Two  valves 
permit  the  blood  to  pass  from  the  auricles  into  the  ventricles,  and  two 
more  guard  the  openings  to  the  two  great  arteries  that  carry  the  blood 
to  the  lungs  and  body.  The  " beating"  of  the  heart  is  due  to  the 
pressing  of  its  small  end  against  the  chest  walls;  this  takes  place  at 
each  contraction  of  the  ventricles.  The  heart  of  a  child  in  its  first 
year  beats  about  120  times  each  minute.  In  the  fourteenth  year  the 
number  of  beats  is  about  85;  in  the  adult,  about  70  or  80. 

376.  Arteries  and  Veins. — The  tubes  that  carry  blood 
from  the  heart  are  called  arteries;  those  bringing  blood 
to  the  heart  are  veins.  The  artery  that  carries  blood 
from  the  left  ventricle  (Fig.  285)  is  called  the  aorta;  this 
artery  and  its  branches  supply  the  body  circulation.  The 
pulmonary  artery,  coming  from  the  right  ventricle,  takes 
blood  to  the  lungs. 

Arteries  are  made  of  3  layers  of  tissue;  the  middle  one 
contains  muscular  fibers.  Thus,  while  the  arteries  are 


ARTERIES  AND  VEINS 


375 


very  strong,  they  are  elastic.  They  expand  as  the  blood 
stream  increases  in  size,  and  contract  as  it  decreases. 
Where  arteries  come  near  the  surface  of  the  body,  the 
wave  of  blood  sent  out  at  each 
contraction  of  the  left  ventricle 
can  be  felt  as  the  pulse.  The 
pulse  reading  is  usually  taken  at 
the  wrist.  Since  the  arteries 
are  elastic,  they  act  as  exten- 
sions of  the  ventricles,  keeping 
the  blood  under  pressure  even 
when  the  ventricles  are  not  con- 
tracted. They  can  do  this  be- 
cause of  the  heart  valves,  which 
prevent  a  flow  of  the  blood  back- 
ward into  the  ventricles. 

Veins  have  thinner  walls  than 
arteries,  and  are  much  less  elas- 
tic. Blood  from  the  body  circu- 
lation enters  the  right  auricle 
through  several  large  veins; 
other  veins  bring  blood  from  the 
lungs  to  the  left  auricle.  Blood 
enters  the  auricles  "by  suction" 
(cf.  §  42),  much  as  lemonade 
enters  a  straw  when  you  remove 
the  air.  When  the  auricle  contracts,  it  forces  its  blood 
into  a  ventricle.  When  the  auricle  is  relaxed,  its  cavity 
increases  in  volume,  and  the  pressure  in  the  cavity  de- 
creases. Blood  cannot  flow  back  into  the  auricle  from 
the  ventricle,  because  the  heart's  valves  prevent  this.  So 


FIG.  285. 

Heart,  Lung,  and  Body  Circula- 
tion. Note  the  course  taken  by 
the  blood. 


376  CIRCULATION  AND  RESPIRATION 

the  pressure  of  the  blood  in  the  veins,  while  feeble,  is 
sufficient  to  force  blood  from  the  veins  into  the  auricles. 
The  body  has  ways  of  helping  the  feeble  blood  pressure 
in  the  veins.  Many  veins  are  so  placed  that  they  are 
easily  compressed  by  the  body  muscles  that  are  near  them. 
Muscles  in  active  use  can  thus  hasten  the  flow  of  blood 
in  the  veins.  Veins  of  this  sort  have  valves  opening 
toward  the  heart,  but  not  away  from  the  heart.  Nature 
takes  care  to  have  the  blood  go  in  the  right  direction. 

377.  Capillaries. — The  capillaries  are  the  smallest  of 
the  blood  vessels  (cf.  §  32),  with  an  average  diameter  of 
about  2^0  °f  an  inch.  While  the  purpose  of  the  blood's 
circulation  is  to  get  food  and  oxygen  to  the  cells,  and  to 
remove  waste  materials  from  the  cells,  yet  the  walls  of 
arteries  and  veins  are  too  thick  to  permit  the  passage  of 
blood  materials.  It  is  only  in  the  capillaries  that  the 
walls  are  thin  enough. 

The  capillaries  extend  to  all  parts  of  the  body.  They  are  in  all 
glands  (cf.  §  358),  for  it  is  through  the  capillaries  that  glands  get  the 
juices  which  they  secrete;  they  are  near  the  digestive  organs,  to  take 
the  digested  food  into  the  blood  (cf.  §  365) ;  they  are  in  the  lungs,  to 
permit  the  blood  to  give  off  its  waste  carbon  dioxide,  and  to  take  in 
oxygen. 

Capillaries  may  be  looked  upon  as  the  tiniest  branches  of  the 
arteries,  carrying  blood  to  the  body;  they  are  also  the  small  beginnings 
of  the  veins,  in  which  the  blood  is  gathered  for  transportation  back  to 
the  heart.  We  can  compare  the  flow  of  blood  through  arteries,  veins, 
and  capillaries  with  the  flow  of  a  stream  of  water  through  a  bed  of 
sand.  The  channel  that  brings  the  water  is  like  an  artery;  the  channel 
through  which  it  flows  after  passing  through  the  sand  is  like  a  vein; 
the  thousands  of  tiny  channels,  by  which  the  water  finds  its  way 
through  the  sand,  correspond  to  the  capillaries. 


THE  BLOOD 


377 


378.  The  Blood. — The  blood  consists  of  two  parts. 
One  is  a  colorless  liquid  called  the  plasma ;  the  other  is  a 
multitude  of  tiny  bodies  called  corpuscles  (cf.  §  341). 
The  plasma  is  made  up  of  water  and  of  dissolved  mate- 
rials. Among  the  dissolved  materials  are  the  blood 
proteids,  made  out  of  the  proteids  digested  by  the  body 
(cf.  §  369).  There  are  also  fats,  dextrose,  salt,  etc. 
Besides  the  foods  and  minerals,  the  plasma  contains 
waste  substances,  chiefly  carbon  dioxide  and  urea. 

The  corpuscles  (Fig.  286)  are  of  2  kinds,  red  and  white. 
The  red  corpuscles  are  much  more  numerous  than  the 
white  ones,  but  smaller. 
As  seen  under  the  micro- 
scope, a  red  corpuscle  is 
a  thin,  yellow  cell  (not 
red),  disc-like  in  shape. 
The  red  corpuscles  are 
generally  in  groups,  like 
"stacks"  of  coins.  The 
groups  appear  red.  Red 
corpuscles  contain  protoplasm  and  a  dark-red  substance 
called  hemoglobin  (from  haima,  " blood,"  and  globe). 
Hemoglobin  forms  a  bright-red  compound  with  oxygen; 
this  is  oxyhemoglobin.  It  is  as  a  part  of  this  compound 
that  oxygen  is  carried  from  the  lungs  to  the  cells.  Bright- 
red  blood  is,  therefore,  blood  with  a  good  supply  of  oxy- 
gen; dark-red  blood  is  poor  in  oxygen. 

White  corpuscles  are  also  single  cells.  Like  amebas 
(cf.  §  333),  they  have  the  power  of  changing  their  shapes 
and  of  moving  about.  They  can  pass  through  the  walls 
of  capillaries  into  the  lymph  (cf.  §  379).  White  corpuscles 


Red 


FIG.  286. 

Blood  Corpuscles,  White  and  Red,  greatly  mag- 
nified. 


378  CIRCULATION  AND  RESPIRATION 

destroy  disease  germs  that  get  between  the  eells>  also  the 
germs  in  the  blood.  When  you  reeeive  a  wound  that 
penetrates  the  skin,  they  form  a  protecting;  wall  around 
the  wound,  and  usually  keep  germs  from  reaching  the 
remainder  of  the  body. 

When  a  wound  bleeds,  it  is  because  a  blood  vessel  has  been  cut.  The- 
blood  at  once  seeks  to  close  the  opening  by  forming  a  thick  mass,  called 
a  clot.  The  clotting,  or  coagulating,  material  is  fibrin;  it  is  formed  out 
of  fibrinogen,  one  of  the  proteids  of  the  blood.  This  substance  coagu- 
lates, even  at  the  blood's  temperature,  much  as  the  white  of  egg  coagu- 
lates when  heated.  If  a  little  absorbent  cotton  is  placed  on  a  wound, 
its  fibers  help  the  fibrin,  and  the  blood  is  coagulated  more  quickly. 

379.  The  Lymph. — The  lymph  is  really  another  form 
of  the  blood.  It  is  made  out  of  the  plasma  and  white 
corpuscles  of  the  blood,  which  pass  through  the  capillary 
walls,  and  out  of  water  and  waste  materials  from  the 
cells.  The  lymph  fills  the  spaces  between  the  cells.  We 
have  learned  (cf.  §  377)  that  the  capillaries  give  oxygen 
and  food  materials  to  the  cells,  and  that  the  cells  give 
waste  materials  to  the  blood.  This  is  not  strictly  true; 
the  capillaries  give  their  materials  to  the  lymph,  and  the 
cells  really  get  their  food  supply  from  the  lymph.  In 
the  same  way  the  cells  discharge  their  waste  into  the 
lymph,  and  the  lymph  passes  it  on  to  the  capillaries. 
Thus  the  capillaries  and  the  cells  really  exchange  material 
through  the  lymph  that  is  between  them. 

The  lymph  has  no  special  pumping  organ  like  the  heart.  For  its 
movement  it  depends  upon  the  pressure  of  certain  organs  of  the  body, 
such  as  muscles.  In  this  respect  the  movement  of  lymph  is  like  the 
movement  of  blood  in  certain  veins  (cf.  §  376).  The  lymph  is  gradually 


RESPIRATION  379 

collected  Into  two  large  tubes,  called  lymphatic  ducts.  By  these  it  is 
discharged  into  the  blood.  The  lymph  of  the  higher  animals  resembles, 
in  many  ways,  the  colorless  blood  of  the  lower  animals,  such  as  insects. 
In  each  case  the  absence  of  a  pumping  organ  and  of  definite  tubes 
makes  the  circulation  slow. 

380.  Excretion. — As    we    have    already    learned    (cf. 
§  358),  glands  secrete  liquids  from  the  blood.    If  the  secre- 
tion is  waste  that  needs  to  be  expelled  from  the  body,  it 
is  called  an  excretion.     Excretion  is  just  as  necessary  as 
;any  body  function,  for  the  wastes  are  poisons  to  the  body. 
The  most  important  wastes  to  be  removed,  aside  from  the 
solid  waste  of  the  alimentary  canal,  are  water,  carbon 
dioxide,  uric  acid,  urea,  and  certain  salts  (cf.  §  220).     The 
carbon  dioxide  is  removed  chiefly  by  the  lungs.     Most  of 
the  other  materials  are  in  solution,  and  are  removed 
by  the  kidneys.    There  are  2  kidneys,  and  they  are 
attached  at  the  back  of  the  abdomen,  one  on  each  side  of 
the  backbone.     They  have  the  shape  of  beans,  and  weigh 
about  5  ounces  each.     The  kidneys  receive  a  large  supply 
of  blood  from  the  heart.     After  removing  the  waste,  they 
return  the  purified  blood  to  the  body.     As  the  solution 
containing  body  waste  is  collected  by  the  kidneys,  it  is 
passed  on  to  the  bladder,  where  it  is  stored  until  it  is 
expelled  from  the  body.     Alcohol  drinkers  are  especially 
liable  to  dangerous  diseases  of  the  kidneys  (cf.  §  371); 
Bright's  disease  is  one  of  them. 

381.  Respiration. — The  need  of  respiration  has  already 
been  given,  and  respiration  has  been  defined  (cf.  §  52). 
We  need  to  respire— 

(1)  To  bring  oxygen  to  the  blood. 


380 


CIRCULATION  AND  RESPIRATION 


(2)  To  remove  carbon  dioxide  from  the  blood.  The 
circulation  of  the  blood  brings  about  oxidation  at  the 
cells,  and  also  carries  the  carbon  dioxide  to  the  lungs. 
The  oxidation  at  the  cells  is  internal  respiration.  The 
exchange  of  gases  between  the  air  and  the  lungs  is  external 
respiration,  or  breathing.  The  chief  organs  of  external 
respiration  are  the  lungs,  and  the  air  passages  which 
connect  the  lungs  with  the  air.  To  these  we  must  add  the 
muscles  and  bones  of  the  chest,  which  aid  in  breathing. 

382.  The  Lungs.— The  lungs  (Fig.  287)  are  two  spongy 
organs  that  hang  in  the  thorax,  and  are  surrounded  by 

two  sacs  of  connec- 
tive tissue.  The  sacs 
are  called  pleurae 
(singular,  pleura). 
The  heart  cavity  is 
between  them.  The 
lungs  are  the  meet- 
ing place  of  air  and 
blood;  hence  we  find 
them  to  be  a  mass  of 
air  passages  and  air 

Diaphragm  ^ /  Cells  OU  tllC  OUC  hSilidj 

and  of  blood  vessels 
on  the  other.  Con- 
nective tissue  holds 
these  together.  The  lungs  are  lined  with  mucous  mem- 
brane, just  as  the  other  air  passages  are  (cf.  §  358).  The 
entrance  of  air  into  the  lungs,  and  its  passage  out  of  the 
lungs,  depend  upon  the  expansion  and  compression  of 


FIG.  287. 

The  Lungs  and  Their  Surroundings,   Including   the 
Diaphragm. 


INSPIRATION  381 

the  lungs;  hence  the  lungs  are  not  rigid,  but  elastic.  The 
air  sacs  of  the  lungs  number  many  millions.  Their  sur- 
face in  an  adult  has  been  estimated  to  be  over  2,000 
square  feet.  This  is  the  floor  area  of  a  room  20  feet  wide 
and  100  feet  long. 

383.  Exchange  of  Gases  in  the  Lungs. — A  large  ar- 
tery (the  pulmonary  artery)  carries  dark-red  blood  from 
the  heart's  right  ventricle  to  the  lungs.     This  blood  is 
spread  out  through  the  network  of  capillaries  that  is  in 
the  air  sacs,  and  loses  its  carbon  dioxide.     At  the  same 
time  it  takes  up  oxygen,  and  becomes  bright  red.     Then 
it  is  carried,  by  the  pulmonary  veins,  to  the  heart's  left 
auricle.     This  pumps  it  into  the  left  ventricle,  by  which 
it  is  forced,  through  the  aorta,  to  the  body. 

The  air  that  enters  the  lungs  contains  21%  oxygen,  78%  nitrogen, 
and  1%  argon.  As  it  leaves  the  lungs,  it  contains  about  16%  oxygen 
and  nearly  5%  of  carbon  dioxide,  water  vapor,  and  other  impurities. 
The  loss  of  oxygen  is  thus  balanced  by  the  gain  in  carbon  dioxide.  The 
amounts  of  nitrogen  and  argon  are  not  changed.  About  1.2  pounds  of 
water  and  1.5  pounds  of  carbon  dioxide  are  exhaled  from  the  lungs  daily. 
As  the  air  exhaled  is  warm,  and  as  the  water  is  in  the  form  of  vapor, 
the  lungs  aid  the  skin  in  removing  heat  from  the  body  (cf.  §  395). 

384.  Inspiration. — The    external    respiration    (breath- 
ing) consists  of  2  acts:  (1)  inspiration,  or  "breathing  in"; 
and  (2)  expiration,  or  "breathing  out."     The  entrance  of 
air  into  the  lungs  (inspiration)  is  brought  about  by  the 
enlarging  of  the  chest.     This  permits  the  air  in  the  lungs 
to  expand,  and  makes  its  density  and  pressure  less  than 
that  of  the  air  outside.     The  outer  air  then  rushes  into  the 
lungs  as  it  would  into  a  vacuum  (cf.  §§6  and  42).     We 
do  not  "suck"  air  into  the  lungs  any  more  than  we  suck 


382  CIRCULATION  AND  RESPIRATION 

soda  water  into  a  tube.  What  we  really  do  is  to  produce 
a  ''partial  vacuum,"  depending  upon  the  air  to  make  the 
pressure  in  the  lungs  the  same  as  that  of  the  outside  air. 

The  expansion  of  the  chest  is  brought  about  in  two  ways.  One  of 
them  is  the  contraction  of  the  diaphragm,  the  muscular  partition  that 
separates  the  thorax  from  the  abdomen.  When  the  diaphragm  con- 
tracts, it  pushes  the  organs  of  the  abdomen  downward,  and  makes  the 
thorax  larger.  This  permits  the  outer  air  to  rush  into  the  lungs.  The 
second  means  by  which  the  expansion  of  the  chest  is  brought  about 
is  by  the  action  of  the  chest  muscles.  When  the  diaphragm  moves 
downward,  these  muscles  pull  the  breastbone  and  ribs  outward. 

385.  Expiration. — The  air  taken  into  the  lungs  during 
inspiration  is  expelled  when  the  muscles  of  the  chest  and 
diaphragm  are  relaxed.     The  ribs  move  downward  and 
inward  of  their  own  weight,  and  the  organs  of  the  abdo- 
men, which  were  crowded  together  during  inspiration, 
expand  again,  and  force  the  diaphragm  up  against  the 
lungs.     As  a  result,  the  elastic  air  cells  of  the  lungs, 
which  were  "puffed  out"  with  air,  are  now  compressed, 
and  the  air  is  forced  back  through  the  air  passages.     The 
air  that  we  inhale  and  exhale  during  ordinary  quiet 
breathing  is  called  tidal  air.     It  is  about  a  pint  (30  cubic 
inches,  or  500  c.c.)  in  volume.      By  making  a  conscious 
effort  we  can  take  in  and  expel  about  100  cubic  inches 
more  air  than  in  quiet  breathing.     The  total  capacity  of 
the  lungs  is  about  one  gallon  (231  cubic  inches,  or  4  liters). 
An  adult ' ' breathes,"  on  the  average,  18  times  in  a  minute. 

386.  Exercises. 

1.  Trace  the  course  of  a  drop  of  blood  from  the  time  it  leaves  the 
left  ventricle  until  it  re-enters  it. 


THE  NOSTRILS  AND  PHARYNX  383 

2.  Is  the  heart  a  suction  pump  or  a  force  pump?     Why  has  the  left 
ventricle  stronger  muscles  than  the  other  heart  chambers? 

3.  Why  does  the  doctor  ' '  take  your  pulse  "  when  you  are  ill?     Why 
does  he  take  your  temperature? 

4.  What  is  meant  by  the  ' '  transfusion  "  of  blood? 

5.  Why  is  the  blood  in  the  veins  ' '  blue  blood ' '  ?  How,  in  an  accident, 
can  you  tell  that  you  have  cut  an  artery  rather  than  a  vein?    Which 
would  be  the  more  serious,  and  why?    On  which  side  of  a  wound  ought 
an  artery  to  be  compressed,  so  as  to  stop  bleeding,  on  the  side  toward 
the  heart  or  on  the  side  away  from  the  heart?     How,  in  the  case  of  a 
cut  vein? 

6.  Draw  a  sketch  showing  the  cells  of  a  capillary  wall  (a  single  layer, 
end  to  end),  and  show  how  an  ameba-like  cell,  such  as  a  white  corpuscle, 
might  get  out. 

7.  What  is  the  special  duty  of  red  corpuscles?    Of  the  white  ones? 
What  body  fluid  forms  the  " matter"  of  a  blister? 

8.  If  you  were  on  a  high  mountain  top,  would  there  be  as  much 
oxygen  in  every  breath  as  at  sea  level?    How  do  you  think  the  body  can 
increase  the  oxidation  of  the  blood  at  high  altitudes? 

9.  When  does  the  heart  have  more  work  to  do,  when  we  stand,  or 
when  we  lie  down?    Why? 

10.  Do  you  think  continued  and  violent  physical  exercise  would 
have  any  effect  on  the  size  of  the  heart?    Why? 

11.  When  a  boy  or  girl  grows  very  rapidly,  how  is  the  heart's  work 
affected?     Ought  violent  exercise  to  be  indulged  in  at  this  time? 

12.  Why  are  you  "out  of  breath"  after  running? 

13.  How  does  a  very  dry  atmosphere  affect  the  organs  of  respira- 
tion?    (Cf.  §249). 

14.  Give  the  course  of  air  in  going  from  the  nostrils  into  the  lungs. 
Give  the  course  of  the  oxygen  from  the  lungs,  through  the  body  cir- 
culation, and  back  again  to  the  lungs. 

387.  The  Nostrils  and  Pharynx. — The  air  that  enters 
the  lungs  goes  through  a  passage  consisting  of  several 
parts;  these  are:  the  nasal  passages,  or  nostrils,  the 
pharynx,  or  throat,  the  larynx,  the  trachea,  or  windpipe, 


384 


CIRCULATION  AND  RESPIRATION 


Tongu 


and  the  bronchial  tubes.     All  of  these  are  lined  with 

mucous  membrane.     In  the  nostrils  (£ig.  288)  the  mucous 

membrane  is  spread 
out  over  a  large  sur- 
face, and  secretes  a 
great  deal  of  mucus. 
The  nostrils,  because 
of  their  length,  serve 
to  warm  the  air  before 
it  reaches  the  wind- 
pipe and  lungs.  The 
mucus  which  they 
secrete  makes  them 
moist,  and  catches  the 
dust  particles  that  are 
in  the  inhaled  air. 
The  air  passages  are 
also  lined,  almost 

everywhere,  with  cilia  (cf.  §  333);  these  sweep  back  the 

dust  particles. 

The  pharynx  was  described  in  §  361.     It  is  separated 

from  the  nostrils,  when  we  swallow  food,  by  the  "soft 

palate. "     The  two  tonsils  are  in  the  sides  of  the  pharynx, 

under  the  lower  jaw  bone. 

388.  The  Larynx  and  Trachea. — The  larynx  (Fig. 
289)  is  a  box  made  out  of  pieces  of  cartilage  placed  at  the 
upper  end  of  the  trachea  (windpipe).  When  we  swallow, 
the  larynx  is  drawn  upward  against  its  cover,  the  epi- 
glottis (cf.  §  361,  Fig.  280) ;  food  passes  over  it  in  going  to 
the  esophagus.  We  can  feel  one  of  the  larynx  cartilages 


FIG.  288. 
The  Mouth  and  the  Nasal  Cavity. 


THE  VOICE 


385 


Uryrw 


(the  ' '  Adam's  apple  ")  at  the  front  of  the  throat.  During 
breathing,  the  larynx  drops  down,  and  there  is  free  com- 
munication between  the  nasal  passages 
and  the  trachea. 

The  trachea  is  a  rounded  tube  about 
an  inch  in  diameter.  It  holds  its  shape 
because  of  a  number  of  pieces  of  cartilage ; 
these  are  bent  in  the  shape  of  a  C.  The 
trachea  divides  into  two  passages,  or 
bronchi,  one  of  which  goes  to  each  lung. 
The  bronchi  divide  and  subdivide  into 
the  bronchial  tubes.  The  smallest  of 
these  end  in  the  air  cells  of  the  lungs. 


FIG.  289. 

The  Larynx,  the  Tra- 
chea, and  the  Bron- 
chial Tubes. 


389.  The  Voice. —  The  larynx  not  only 
forms  the  opening  from  the  throat  to  the 
trachea,  but  it  also  holds  the  chief  organs 
of  the  voice,  the  vocal  cords  (Fig.  290).     The  vocal  cords 
are  two  strips  of  connective  tissue  fastened  to  the  cartilages 


Producing  Sound 


Quiet  Breathing 


FIG.  290. 
The  Vocal  Cords. 


of  the  larynx.  When  not  in  use  they  are  drawn  aside, 
leaving  a  V-shaped  opening.  The  cords  are  brought  into 
use  by  means  of  muscles.  These  act  on  the  cartilages  of 


386  CIRCULATION  AND  RESPIRATION 

the  larynx,  and  bring  the  edges  of  the  cords  near  each 
other.  The  air  that  passes  through  the  larynx  makes  the 
cords  vibrate,  producing  sounds.  The  sounds  are  soft  or 
loud  according  to  the  amount  of  air  used.  . 

The  pitch  of  the  voice  (cf.  §  192)  depends  chiefly  upon 
the  degree  of  tightness  of  the  vocal  cords,  and  upon  their 
length.  When  the  cords  are  tightly  drawn,  and  short, 
they  vibrate  more  rapidly  than  when  loose  and  long; 
hence  they  produce  sounds  of  higher  pitch.  A  man  has 
a  larger  larynx  than  a  woman  has,  and  his  vocal  cords  are 
larger  and  longer.  As  a  result  his  voice  is  of  lower  pitch. 

390.  Speech. — We  use  the  vocal  cords  in  ordinary  speaking  and 
singing,  yet  we  can  "whisper"  words  without  using  the  vocal  cords 
at  all.    We  make  the  whispered  words  with  the  throat,  tongue,  teeth, 
and  lips.     When  we  want  to  give  loudness  and  pitch  to  our  words,  we 
force  the  necessary  amount  of  air  over  the  vocal  cords.     The  throat, 
mouth,  and  nostrils  also  strengthen  the  sounds  that  come  from  the 
vocal  cords.     The  quality  of  a  voice  is  that  peculiarity  which  distin- 
guishes one  voice  from  another.     By  means  of  it  we  recognize  the 
voices  of  our  friends.     Voice  quality  depends  on  the  special  shape  of 
the  air  passages  and  mouth  in  each  person,  and  on  the  peculiar  way  in 
which  each  of  us  uses  them  in  speaking  and  singing. 

Vowels,  or  "vocals"  (a,  e,  i,  o,  u,  and  y)  are  the  vocal-cord  sounds 
that  are  changed  least  by  the  mouth,  tongue,  lips,  etc. ;  consonants  are 
greatly  altered  forms  of  these  sounds. 

391.  Care   of   the   Organs    of    Respiration. — In   our 

breathing,  as  in  eating  and  drinking,  we  are  taking  ex- 
ternal material  into  the  body.  If  there  are  disease  germs 
in  this  material,  they  have  opportunity  to  develop  and  to 
cause  disease.  We  therefore  need  to  guard  against 
throat  and  lung  diseases,  as  well  as  against  typhoid.  The 


CARE  OF  THE  ORGANS  OF  RESPIRATION  387 

surest  way  to  keep  the  organs  of  respiration  in  good  health 
is  to  learn  good  methods  of  breathing,  and  to  breathe 
good  air  (review  §§  246  to  249).  Our  breathing  should  be 
"full,"  and  not  "shallow";  that  is,  it  should  give  all  the 
lung  cells  opportunity  to  carry  on  the  exchange  of  gases, 
and  not  only  a  part  of  them.  It  is  the  unused  portions 
of  the  lungs  that  are  most  liable  to  disease.  We  should 
stand  and  sit  erect,  with  the  abdomen  drawn  in,  and  the 
chest  expanded,  at  every  inspiration.  If  we  are  confined 
indoors  because  of  our  work,  we  should  go  out  of  doors, 
or  to  an  open  window,  every  little  while,  and  should 
breathe  deeply  of  fresh  air. 

We  should  all  breathe  through  the  nostrils,  and  not 
through  the  mouth.  The  nostrils  remove  dust  and  the 
disease  germs  that  cling  to  it  (cf.  §  387),  while  mouth- 
breathing  permits  the  germ-covered  dust  to  enter  the 
throat,  windpipe,  and  lungs.  Mouth-breathers  are  espe- 
cially likely  to  have  throat  and  lung  diseases.  Some 
children  have  growths  in  the  nasal  passages  ("nasal 
polyps")  or  in  the  pharynx  ("adenoids");  these  close 
the  nasal  openings  to  the  lungs,  and  cause  mouth-breath- 
ing. All  such  growths  should  be  removed  by  a  competent 
surgeon,  for  they  often  bring  on,  not  only  throat  and  lung 
diseases,  but  also  deafness;  and  they  make  many  a  child 
appear  stupid,  when  he  is  really  ill. 

Colds  require  the  greatest  care,  for  they  lower  the  power  of  the 
body,  especially  of  the  organs  of  respiration,  to  resist  disease,  and  make 
these  organs  fall  an  easy  prey  to  pneumonia,  consumption,  diphtheria, 
etc.  The  practice  of  deep  breathing  is  a  great  aid  in  preventing  colds. 

Tobacco  smoke  irritates  the  throat  and  lungs  by  clogging  up  their 
delicate  membranes  with  soot.  Cigarettes,  especially,  are  harmful 


388 


CIRCULATION  AND  RESPIRATION 


to  the  organs  of  respiration.  Their  smoke  contains  not  only  the  poison 
of  tobacco  (nicotine),  and  poisonous  gases  like  carbon  monoxide 
("coal  gas"),  but  also  very  irritating  organic  compounds  called 
aldehydes,  which  bring  on  the  "hacking"  cough  of  the  cigarette  user. 

Alcoholic  liquors  are  likely  to  bring  on  weakness  of  the  lungs,  so  that 
the  drinker  is  easily  attacked  by  pneumonia  and  consumption. 

Tight  clothing  is  a  serious  hindrance  to  good  breathing.  If  clothing 
is  too  tight  about  the  chest,  the  chest  cannot  be  enlarged  properly  in 
inspiration.  If  it  is  too  tight  at  the  waist,  it  compresses  the  diaphragm, 
the  ribs,  and  the  organs  of  the  abdomen,  and  makes  full  breathing 
impossible. 

392.  The  Skin. — The  skin  .(Fig.  291)  serves  as  an  out- 
side covering  for  the  body,  protecting  it  from  hurts,  and 
from  the  germs  of  disease  that  are  constantly  in  the  air. 

It  consists  of  2  layers:  (1) 
the  true  skin,  or  dermis; 
(2)  the  outer  skin,  or  cuticle. 
The  cuticle  is  also  called  the 
epidermis,  meaning,  "upon 
the  dermis"  (cf.  §309).  , 

The  epidermis  consists  of 
transparent  cells,  and  has  no 
nerves  or  blood  vessels.  It 
forms  a  tough  outside  cover- 
ing. The  lower  layer  of  epi- 
dermis cells  is  in  contact  with 
lymph  (cf.  §  379),  and  from 
it  gets  the  nutriment  that  is 
needed  for  the  making  of  new 
cells.  These  take  the  place  of  those  rubbed  off  at  the 
surface  (cf.  §  223).  Where  the  skin  is  put  to  rough  use, 
as  in  the  palms  of  the  hands  and  the  soles  of  the  feet,  the 


Fia.  291 
Layers  of  the  Skin,  Greatly  Magnified. 


THE  HAIR  AND  NAILS  389 

epidermis  becomes  thick,  forming  a  callus.  A  corn  is  a 
thick  layer  of  epidermis  cells  formed  at  one  spot.  It 
hurts  because  it  is  pressed,  by  the  shoe,  into  the  true  skin 
beneath. 

The  dermis,  or  true  skin,  is  much  thicker  than  the 
epidermis.  It  is  made  up  of  tough  fibers  of  connective 
tissue,  and  has  blood  vessels  and  nerves.  The  surface  of  the 
dermis  has  little  elevations  called  papillae,  some  of  which 
contain  the  bodies  that  bring  about  the  senses  of  touch 
and  of  temperature  (cf.  §  410).  On  the  inner  side  of  the 
hands  and  fingers  the  papillae  are  arranged  in  rows .  A  layer 
of  fat  is  generally  found  under  the  dermis  (cf.  §  369). 

The  color  of  the  skin  is  due  to  coloring  matter  in  the 
lower  layers  of  epidermis  cells.  When  the  skin  is  tanned 
by  wind  and  sun,  the  coloring  matter  is  increased. 
Freckles  are  spots  of  coloring  matter  in  the  epidermis. 

393.  The  Perspiration. — The  perspiration  is  the  liquid 
poured  out  upon  the.  skin  by  the  sweat  glands  (Fig.  291). 
These  glands  are  tubes  coiled  at  their  lower  ends,  and  set 
into  the  lower  part  of  the  dermis.     Their  purpose  is  to 
cool  the  body  (cf.  §  74).     It  is  only  when  we  are  very  hot 
that  the  sweat  collects  on  the  skin  in  drops  (sensible 
perspiration).     Ordinarily  the  perspiration  is  not  noticed 
(insensible  perspiration).     The  sweat  glands  are  under 
the  control  of  the  nervous  system ;  much  or  little  perspira- 
tion is  given  off,  according  as  the  body  needs  to  give  off 
heat,  or  to  retain  it. 

394.  The  Hair  and  Nails.— The  hair  and  nails  (Fig.  292) 
are  made  of  cells  of  the  epidermis,  but  they  have  taken 


390 


CIRCULATION  AND  RESPIRATION 


Epidermis 


special  forms.  A  hair  is  a  tiny  tube,  formed  in  a  pocket  of 
the  dermis.  The  part  projecting  from  the  skin,  like  the 
•epidermis  itself,  has  neither  blood  vessels  nor  nerves.  But 

the  inner  end  of  the  hair 
is  in  the  true  skin,  and 
is  kept  growing  by  the 
formation  of  new  cells. 
These  are  nourished  by 
the  lymph  of  the  dermis. 
Tiny  muscles  in  the  hair 
"pits"  sometimes  cause 
the  hair  to  "stand  on 
end/'  causing  "goose- 
flesh."  The  hair  covers 
nearly  the  whole  body. 


FIG.  292. 
Structure  of  the  Nails  and  the  Hair. 


In  the  hair  pits  there  are  glands  that  secrete  an  oil  for  the  hair; 
these  are  the  oil  glands,  or  sebaceous  glands.  The  oil  softens  the  skin 
and  the  hair.  Brushing  the  hair  helps  the  oil  glands  in  their  work,  for 
it  spreads  the  oil  along  the  outside  of  the  hair. 

Dandruff  is  a  disease  of  the  sebaceous  glands  and  scalp.  It  is  prob- 
ably due  to  bacteria,  and  may  spread  from  one  person  to  another. 
Only  clean  combs  and  brushes  should  ever  be  used  for  the  hair.  If 
we  pull  a  hair  out  without  destroying  the  cell  that  produces  it,  a  new 
hair  will  grow.  In  baldness  the  cells  lose  the  power  of  producing  new 
hair.  The  cause  of  all  baldness  is  not  known,  but  much  of  it  seems  to 
result  from  dandruff,  or  from  a  lack  of  fat  in  the  scalp. 

The  nails  are  plates  of  tough  epidermis  that  grow  out  of 
depressions  in  the  dermis.  They  grow  in  length  and 
thickness  as  new  epidermis  cells  are  formed  at  their  inner 
ends,  or  roots.  The  older  part  of  a  nail  is  transparent; 
the  blood  vessels  beneath  it  make  it  appear  pink. 


FUNCTIONS  OF  THE  SKIN  391 

395.  Functions  of  the  Skin. — Some  of  the  functions 
of  the  skin  have  already  been  given.  It  is,  first  of  all,  a 
covering  for  the  body;  it  also  contains  the  structures 
that  act  upon  the  nerves  of  touch  (cf.  §  392).  In  giving 
off  perspiration  it  is  an  organ  of  excretion,  like  the  kidneys 
(cf.  §  380).  It  is  likewise  one  of  the  regulators  of  the 
body's  temperature:  the  skin  and  the  lungs  together 
(cf.  §  383)  enable  the  body  to  cast  off  the  heat  it  does  not 
need. 

The  body  remains  at  the  normal  temperature  (98.6°  F.) 
whether  we  exercise  or  remain  at  rest,  when  the  weather 
is  cold  as  well  as  when  it  is  hot.  This  temperature  there- 
fore represents  a  condition  of  balance  in  the  body's  heat 
supply:  at  98.6°  F.  we  gain  heat  and  lose  heat  in  equal 
amounts.  When  we  are  warm,  the  blood  rushes  to  the 
surface  of  the  body.  The  skin  then  radiates  heat  rapidly; 
a  rapid  flow  of  perspiration  also  takes  place.  By  these 
means  the  blood  is  cooled,  and  the  body's  heat  is  lowered. 

If  the  heat  of  the  body  needs  to  be  saved,  as  when  we  are 
in  a  cool  room,  the  blood  vessels  near  the  surface  grow 
smaller,  and  less  blood  comes  to  the  skin.  Thus  the  body 
loses  less  heat.  If  the  lack  of  blood  near  the  skin  con- 
tinues for  a  time,  we  feel  cold.  Then,  if  we  are  wise,  we 
'raise  the  temperature  of  the  room,  or  wear  warmer  cloth- 
ing. When  the  blood  vessels  remain  tightly  closed,  as  in 
some  forms  of  fever,  we  have  a  feeling  of  cold  (a  chill), 
even  when  the  body  has  heat  that  needs  to  be  given  off. 

Bathing. — The  need  of  bathing  has  already  been  given  (cf.  §  223). 
The  skin  becomes  covered  with  body  wastes  from  the  evaporated 
perspiration,  with  oil  from  the  sebaceous  glands,  with  dust  from  the 
clothing  and  the  air,  and  with  dead  epidermis.  The  best  kind  of  a 


392  CIRCULATION  AND  RESPIRATION 

bath  for  removing  this  accumulation  is  a  warm  bath;  it  should  be  taken 
at  night,  if  possible.  Warm  baths  taken  in  the  daytime,  unless  they 
are  followed  by  a  cold  shower  bath,  or  by  a  dash  of  cold  water,  may 
make  one  liable  to  colds  (cf.  §  391).  A  warm  bath  at  night  also  aids 
in  bringing  on  a  good  night's  sleep. 

In  the  morning,  when  we  wish  to  be  aroused  for  the  day's  work, 
especially  if  we  must  go  out  into  the  cold,  a  cold  bath  is  the  best.  The 
cold  water  gives  the  body  a  shock,  in  which  the  blood  is  driven  inward 
from  the  skin;  but  after  a  vigorous  rubbing  the  skin  glows.  This  is 
due  to  the  "  reaction,"  as  the  blood  re-enters  the  skin. 

Many  persons  cannot  endure  the  shock  of  a  tub  of  cold  water;  they 
do  not  have  a  proper  reaction,  and  feel  chilly.  Such  persons  can,  as  a 
rule,  take  a  cold  "sponge"  bath,  in  which  the  water  is  applied  rapidly 
with  a  wet  sponge  or  washcloth.  Vigorous  rubbing  with  a  dry,  rough 
towel  will  bring  about  the  "  reaction." 

396.  Summary. — The  blood  carries  oxygen  and  digested  food  to  the 
cells,  distributes  the  body's  heat,  and  acts  as  the  sewer  for  cell  wastes. 

The  organs  of  circulation  are  the  heart,  arteries,  veins,  and  capil- 
laries; also  the  spaces  containing  the  lymph. 

The  heart  has  4  chambers,  each  of  which  can  be  made  smaller  by 
the  contraction  of  strong  muscles. 

The  right  auricle  receives  blood  from  the  body  circulation,  and  forces 
it  into  the  right  ventricle.  This,  in  its  turn,  forces  the  blood  to  the 
lungs  to  be  oxidized. 

The  left  auricle  receives  purified  blood  from  the  lungs,  and  forces 
it  into  the  left  ventricle.  This  forces  it,  through  the  artery  called  the 
aorta,  into  the  body  circulation. 

The  valves  of  the  heart  make  the  blood  flow  in  one  direction. 

Arteries  carry  blood  from  the  heart;  veins  carry  it  to  the  heart; 
capillaries  carry  it  from  arteries  to  veins  through  the  body's  tissues. 

Arteries  have  very  elastic  walls,  and  are  very  strong.  Some  veins 
have  valves  that  open  toward  the  heart;  the  circulation  in  such  veins 
is  helped  by  the  pressure  of  muscles  near  them. 

The  blood  consists  of  the  plasma  and  corpuscles.  Corpuscles  are 
red,  and  white.  Red  corpuscles  contain  hemoglobin,  which  combines 


SUMMARY  393 

with  oxygen  at  the  lungs.  White  corpuscles  are  like  amebas.  They 
destroy  bacteria. 

The  coagulated  material  of  a  blood  clot,  which  closes  a  wound,  is 
fibrin,  formed  out  of  one  of  the  proteids  of  the  blood. 

Lymph  is  a  form  of  blood  that  exists  outside  of  the  organs  of  rapid 
circulation.  It  has  no  red  corpuscles.  In  supplying  the  cells,  the 
capillaries  give  their  food  material  to  the  lymph,  and  this  gives  it  to  the 
cells. 

Excretion  is  the  secretion  of  waste  solutions,  so  that  they  may  be 
removed  from  the  body.  The  chief  excreting  organs  are  the  kidneys. 
The  skin  excretes  waste  in  the  perspiration. 

Respiration  brings  oxygen  to  the  blood,  and  removes  carbon  dioxide 
from  the  blood. 

The  chief  organs  of  respiration  are  the  two  lungs  and  the  air  pas- 
sages. The  pleurae  are  sacs  that  surround  the  lungs.  The  lungs 
contain  a  multitude  of  air  cells. 

In  the  lungs  the  air  loses  about  %  of  its  oxygen,  and  takes  up  car- 
bon dioxide  in  its  place. 

In  inspiration  the  chest  is  enlarged,  and  the  outside  air  rushes  into 
the  lungs. 

In  expiration  the  diaphragm  and  ribs  are  crowded  against  the  lung 
cavity,  and  force  out  the  air. 

The  air  passages  include  the  nasal  passages,  the  pharynx,  the  larynx, 
the  trachea,  and  the  bronchial  tubes.  All  are  lined  with  mucous  mem- 
brane. 

The  larynx  contains  the  vocal  cords.  In  speaking  and  singing  we 
make  sounds  with  the  throat,  tongue,  lips,  teeth,  and  nostrils,  as  well 
as  with  the  vocal  cords. 

We  should  have  good  habits  of  breathing,  and  should  breathe  good 
air.  Mouth  breathing  is  dangerous. 

Colds,  tobacco,  alcohol,  and  tight  clothing  are  all  sources  of  danger 
to  the  organs  of  respiration. 

The  skin  consists  of  epidermis  and  dermis.  The  sense  of  touch  is 
in  the  papillae  of  the  dermis. 

Perspiration  is  secreted  (excreted)  by  the  sweat  glands  of  the 
•  dermis. 


394  CIRCULATION  AND  RESPIRATION 

Hair  and  nails  are  special  forms  of  epidermis;  they  grow  from  pits 
("roots")  in  the  dermis. 

The  functions  of  the  skin  are  to  cover  the  body,  to  assist  in  the  sense 
of  touch,  to  excrete  perspiration,  and  to  help  regulate  the  body's 
temperature. 

Bathing  restores  to  the  skin  a  fresh,  clean  surface,  so  that  it  can 
carry  out  its  functions. 

397.    Exercises. 

1.  With  what  organs  of  speech  do  you  make  the  sounds  of  k,  I,  g,  d, 
t,  m,  s,  and/?     Find  out  how  you  make  the  sounds  of  all  the  letters  of 
the  alphabet,  and  make  a  list  of  them,  putting  together  all  the  letters 
that  seem  more  or  less  alike. 

2.  If  you  feel  chilly,  a  few  deep  breaths,  especially  if  you  "hold 
your  breath"  while  the  lungs  are  full,  will  make  you  warm.     Tell  why.. 

3.  Why  should  one  go  to  bed  when  he  has  a  bad  cold? 

4.  What  harm  is  done  by  the  wearing  of  tight  belts? 

5.  What  is  the  danger  in  the  taking  of  a  hot  bath,  and  then  going: 
out  into  the  cold  air?    How  may  the  danger  be  made  less? 

6.  What  are  the  uses  of  the  finger  nails? 

7.  How  can  a  person's  finger  prints  be  used  in  identifying  him? 

8.  Why  is  nasal  catarrh  so  common  a  disease? 

9.  How  does  a  dog  cool  his  body  when  he  is  hot? 

10.  Alcohol  drives  the  blood  into  the  skin,  giving  a  temporary  feel- 
ing of  warmth.     Is  a  drinker  wise  in  "fortifying"  himself  with  liquor 
before  going  out  into  the  cold? 

11.  Tramps  often  keep  themselves  warm  in  cold  weather  by  putting 
a  sheet  or  two  of  newspaper  inside  their  coats;  explain.     How  could 
you  use  this  fact  to  keep  yourself  warm,  if  you  found  the  bedding  of 
your  room  insufficient? 


CHAPTER  XIX 

THE  NERVES  AND  THE  SENSE  ORGANS 

398.  The  Nervous  System. —  In  studying  a  complex 
structure  like  the  human  body,  we  need  to  consider  it 
part  by  part,  and  system  by  system.  We  must  remem- 
ber, however,  that  the  body  is  not  simply  one  structure 
added  to  another,  but  that  it  is  a  complete  organism,  with 
many  parts  acting  together  harmoniously.  The  eye, 
hand,  and  foot  have  each  a  separate  function,  but  all  can 
combine  to  do  one  thing,  say,  to  make  a  "drop  kick"  in 
football,  or  to  run  a  sewing  machine.  The  movements 
of  the  eye,  hand,  and  foot  are  under  the  control  of  the 
will,  but  there  are  many  activities  of  the  body  that  pro- 
ceed without  our  notice  and  without  any  effort  of  the 
will.  Examples  of  these  are  the  beating  of  the  heart,  the 
movements  of  the  ribs  and  diaphragm  in  respiration,  the 
secretion  of  saliva,  gastric  juice,  and  bile  when  they  are 
needed.  Our  food  is  under  our  control  until  the  muscles 
of  the  throat  have  contracted  in  swallowing;  after  that  it 
is  in  the  control  of  involuntary  muscles.  How  does  each 
organ  of  the  body  know  when  to  perform  its  function, 
how  much  effort  to  put  forth,  and  when  to  stop?  The 
answer  is  that  the  different  organs  are  in  communication 
with  one  another,  like  the  stations  of  a  telegraph  system, 
or  the  houses  on  a  telephone  line.  When  there  is  a  need 
for  the  performing  of  a  function,  the  organ  concerned 
receives  notice  of  the  need,  and  sets  about  doing  its  par- 

395 


396  THE  NERVES  AND  THE  SENSE  ORGANS 

ticular  work.  When  the  demand  is  over,  the  organ  re- 
ceives notice,  and  stops  its  work.  This  regulation  of  the 
body  by  communication  between  its  parts  is  the  work  of 
the  nervous  system. 

The  nervous  system  is  studied  in  two  divisions : 

(1)  The  central  nervous  system,  consisting  of  the  brain 
and  spinal  cord,  and  the  nerves  that  start  from  these 
structures; 

(2)  The  sympathetic  nervous  system,  which  puts  the 
internal  organs  into  communication  with  one  another  and 
with  the  central  system. 

399.  Nerve  Cells  and  Their  Structure.—  The  parts  of 
the  nervous  system  are  made  up  of  nerve  tissue,  just  as 
muscles  are  made  up  of  muscle  tissue.  The  unit  of  nerve 
tissue  is  the  nerve  cell,  or  neuron  (Fig.  293).  This  con- 


Terminal 
Brariches 


Fig.  293. 
A  Neuron,  or  Nerve  Cell. 

sists  of  two  parts,  the  cell  body,  or  cell  proper,  and  ex- 
tensions of  the  cell  body.  The  cell  body  looks  much  like 
other  cells,  except  that  it  has  a  grayish  color.  The  ex- 
tensions of  the  cell  body  are  of  two  sorts.  One  of  them 
is  the  long,  slender  nerve  fiber,  or  axon.  Some  cells  have 
one  of  these;  others  have  two.  Cells  that  have  one  axon 
have  also  shorter  extensions,  or  dendrites.  Dendrites 


NERVE  CELLS  AND  THEIR  STRUCTURE  397 

branch  like  the  boughs  or  roots  of  trees,  and  so  get  their 
name :  dendron  means  ' '  tree. ' ' 

The  nerve  fiber,  or  axon,  consists  of  a  central  part 
called  the  axis  cylinder,  and  of  two  protective  coverings,  or 
sheaths.  The  axis  cylinder  is  an  extension  of  the  proto- 
plasm of  the  cell  body,  and,  like  the  cell  body,  is  gray. 
The  coverings  of  the  axis  cylinder  are  usually  white.  A 
bundle  of  nerve  fibers  is  what  we  commonly  call  a  nerve. 
Nerve  messages  are  carried  by  the  axis  cylinders  of  the 
axons.  A  nerve  message  is  also  called  a  stimulus  (plural, 
stimuli;  cf.  §  206)  and  a  nerve  impulse. 

Nerve  fibers  are  of  3  kinds,  according  to  their  use: 
(1)  those  that  carry  messages  from  an  organ  to  the  brain 
or  spinal  cord;  (2)  those  that  carry  messages  back  to  the 
organs;  (3)  those  that  connect  the  other  two.  The  nerve 
fibers  carrying  messages  to  the  brain  are  called  afferent 
fibers,  or  sensory  fibers.  They  are  called  afferent  fibers 
from  a  word  meaning  "carrying  to;"  they  are  called 
sensory  fibers  because  they  carry  the  stimuli  received  by 
the  senses  to  the  central  nervous  system.  Nerve  fibers 
of  the  second  class  are  called  efferent  fibers,  from  a  word 
meaning  "carrying  away  from."  These  fibers  carry 
messages  from  the  central  system  to  the  organs.  Efferent 
fibers  are  also  called  motor  fibers,  because  through  them 
comes  the  message  telling  the  organ  to  act,  or  move. 
The  nerve  fibers  that  connect  afferent  and  efferent  fibers 
are  called  associating  fibers. 

Nerve  tissue  may  be  in  separate  neurons,  or  it  may 
consist  of  groups  of  neurons,  called  ganglia  (singular, 
ganglion,  a  "knot").  The  brain  and  spinal  cord  consist 


398 


THE  NERVES  AND  THE  SENSE  ORGANS 


of  large  groups  of  neurons;  there  are  smaller  groups  in 
different  parts  of  the  body. 


Fissure 
of  Sylvius 


Medulla  Oblongata 
or  Bulb 


400.  The  Brain  and  Its  Parts.— The  brain  is  the 
largest  part  of  the  nervous  system  (Fig.  294).  It  weighs 
about  3  pounds;  in  exceptional  cases,  4  pounds.  In  other 

mammals  there  is 

Cerebrum-     ^^W^Jl«fc-  a    distinct    front 

portion,  or  fore- 
brain,  called  the 
cerebrum.  In 
man  this  is  the 
upper  portion. 
There  is  also  a 
midbrain  and  a 
hindbrain.  The 
hindbrain  con- 
sists of  the  cere- 
bellum, the  pons, 

and  the  bulb.  The  bulb  is  also  called  the  medulla  oblongata. 
The  cerebrum  is  gray  because  of  the  cell  bodies  on  its 
surface  (cf.  §  399).  Its  interior  is  white,  and  consists  of 
bundles  of  nerve  fibers  ("nerves")-  The  surface  of  the 
cerebrum  of  an  adult  person  has  a  great  many  folds,  or 
convolutions;  these  greatly  increase  its  area.  The  in- 
creased area  of  the  cerebrum  is  needed  as  its  cells  increase 
in  number.  A  deep  dent  from  front  to  back  divides  the 
cerebrum  into  a  right  and  a  left  hemisphere.  All  the 
parts  of  the  cerebrum  are  connected  by  nerve  fibers,  and 
a  multitude  of  fibers  connect  the  cerebrum  with  the  mid- 
brain,  hindbrain,  and  spinal  cord,  as  well  as  with  the 


Fig.  294. 
The  Parts  of  the  Brain. 


THE  SPINAL  CORD  399 

sense  organs.     The  cerebrum  is  the  organ  of  the  mind. 

Through  it  we  get  the  sensations  of  heat,  light,  sound, 
touch,  taste,  etc.,  and  the  use  of  our  voluntary  muscles. 
Twelve  pairs  of  nerves  (cranial  nerves)  pass  from  the 
front  of  the  cerebrum  directly  (that  is,  without  going 
through  the  spinal  cord)  to  the  head,  neck,  and  trunk. 

The  midbrain  is  a  rounded  body  lying  under  the  cerebrum,  and 
connecting  the  forebrain  with  the  hindbrain. 

The  cerebellum  (meaning,  "little  cerebrum")  is  the  largest  body  of 
the  hindbrain,  and  occupies  most  of  the  space  inside  the  "base  of  the 
skull."  It  is  covered  over  by  the  back  lobes  of  the  cerebrum,  and  its 
surface  looks  much  like  that  of  the  cerebrum.  The  cerebellum  seems 
to  have  special  control  of  muscular  movements,  making  the  muscles 
contract  properly  and  in  pairs  (cf.  §  355).  It  thus  causes  the  move- 
ments of  the  body  to  be  orderly  and  regular. 

The  pons  (from  the  Latin  word  for  "a  bridge")  is  in  front  of  the 
cerebellum,  and  consists  largely  of  bands  of  nerve  fibers.  These  con- 
nect the  cerebrum,  cerebellum,  and  bulb. 

The  bulb,  or  medulla  oblongata,  is  really  the  enlarged  upper  end  of 
the  spinal  cord,  although  it  is  within  the  cranium.  It  is  below  the 
cerebellum,  and  consists  of  ganglia  of  the  nerve  cells  and  nerve  fibers 
that  form  the  connection  between  the  spinal  cord  and  the  brain. 

401.  The  Spinal  Cord.—  The  spinal  cord  (Fig.  295)  is  a 
column  of  nerve  tissue  about  %  of  an  inch  thick;  in  the 
adult  it  occupies  the  cavity  of  the  spinal  column  down  to 
the  bottom  of  the  20th  vertebra.  The  cord  is  not  round, 
but  has  two  lengthwise  depressions  (one  in  front  and  one 
in  back)  that  make  a  cross  section  of  it  look  like  a  capital 
H.  The  outside  of  the  spinal  cord  is  white,  from  the 
coverings  of  its  nerve  fibers.  The  inside  of  the  cord  con- 
sists of  gray  cells,  and  its  section  also  resembles  an  H. 
At  its  upper  end  the  cord  enters  the  skull,  and  is  enlarged 


400 


THE  NERVES  AND  THE  SENSE  ORGANS 


to  form  the  bulb.  The  cord's  lower  end  is  continued  in 
large  nerve  trunks,  which  supply  the  hips  and  lower 
limbs. 

There  are  31  pairs  of  nerves  attached  to  the  spinal  cord.  Each  of 
these  joins  the  cord  by  a  dorsal  (back)  and  a  ventral  (front)  root.  The 
two  roots  come  together  in  a  single  " nerve"  before  they  pass  out  of 
the  vertebrae,  but  their  fibers  remain  separate,  and  have  different 
functions.  The  fibers  of  the  dorsal  roots  are  afferent,  and  carry 


Efferent 
Fibre 


Spinal 
Cord 


Fig.  295. 
The  Spinal  Cord  and  its  Connections. 


messages  to  the  cord  and  brain;  the  fibers  of  the  ventral  roots  are 
efferent,  and  carry  messages  to  the  organs. 

The  spinal  cord  and  brain  are  admirably  protected  by  the  vertebrae 
and  the  cranium.  They  are  surrounded  by  3  membranes,  which  come 
between  them  and  the  bones  themselves.  One  of  the  membranes  con- 
tains a  watery  liquid;  this  acts  as  a  cushion  to  prevent  injury  from 
sudden  shocks. 

402.  The  Sympathetic  System. —  We  have  seen  that 
the  brain  and  spinal  cord  are  the  great  nerve  centers  of 
the  body,  and  that  they  consist  of  a  multitude  of  nerve 
cells  gathered  together  in  large  ganglia  and  nerve  trunks. 
Besides  this  central  system,  the  body  has  another  group 
of  nerve  structures,  called  the  sympathetic  system.  This 


THE  SYMPATHETIC  SYSTEM  401 

system  is  smaller  than  the  central  system,  but  is  very 
important.  It  has  for  its  special  work  the  control  of  the 
internal  organs,  such  as  the  stomach,  liver,  etc.  It  also 
controls  the  skin,  with  its  blood  vessels  and  sweat  glands. 
In  addition,  it  has  charge  of  other  parts  of  the  body  that 
are  not  reached  directly  by  the  brain  and  the  spinal  cord. 

The  sympathetic  system  gets  its  name  from  the  fact  that  by  con- 
necting the  different  internal  organs  it  sees  to  it  that  they  act  "in 
sympathy  with"  one  another. 

While  the  ganglia  of  the  sympathetic  system  are  found  in  many 
parts  of  the  body,  they  are  most  abundant  in  two  chains  that  are  placed 
in  front  of  the  spinal  column,  one  on  each  side  of  it.  The  plexuses  are 
very  complex  ganglia  of  the  sympathetic  system.  The  solar  plexus  is 
one  of  these;  it  has  been  called  the  " brain  of  the  abdomen."  It  is 
behind  the  "pit  of  the  stomach,"  and  is  so  important  for  all  the  com- 
mon body  functions  that  there  is  danger  of  instant  death  if  it  is  injured. 
For  this  reason  a  blow  in  the  region  of  the  stomach  is  very  serious. 

The  sympathetic  system  is  not  independent  of  the 
central  system,  but  is  a  part  of  it.  This  is  illustrated  by 
a  simple  case.  When  food  gives  a  stimulus  to  the  afferent 
nerve  fibers  of  the  stomach,  they  carry  the  message  to 
certain  sympathetic  ganglia.  The  ganglia  cannot  turn 
the  message  back  to  the  gastric  glands,  directing  them  to 
secrete  the  gastric  juice;  the  ganglia  must  send  the 
message  on  to  the  central  system.  Then,  if  the  demand 
is  a  normal  one,  such  as  the  call  for  gastric  juice,  the  lower 
parts  of  the  central  system  (the  spinal  cord  or  the  bulb, 
for  example)  can  send  the  efferent,  or  motor,  impulses. 
The  return  message  goes  through  efferent  axons  and  the 
sympathetic  ganglia  to  the  secreting  glands.  In  such  a 
case  the  upper  brain  (cerebrum)  has  no  part  in  the 


402  THE  NERVES  AND  THE  SENSE  ORGANS 

operation.  But  if  the  sensation  in  the  stomach  is  not  a 
normal  one,  but  one  of  injury,  the  message  goes  to  the 
cerebrum,  and  we  feel  pain. 

'This  action  of  the  sympathetic  system  upon  the  blood  vessels  of  the 
skin  is  well  illustrated  by  the  phenomenon  of  blushing.  When  we 
have  some  unusual  emotion  (it  may  come  from  an  insult  or  a  com- 
pliment), the  sympathetic  nerves  cease,  for  a  time,  to  control  the  blood 
vessels  that  come  to  the  skin.  As  a  result,  the  blood  rushes  into  them, 
•until  the  skin  is  red  and  hot.  Then  the  sympathetic  system  gets  back 
its  control  over  the  blood  vessels,  causes  them  to  contract,  and  turns 
the  excess  of  blood  away  from  the  skin.  There  is' a  very  close  con- 
nection between  our  emotions  and  the  way  in  which  our  internal 
organs  carry  out  their  work.  Thus,  unpleasant  emotions,  such  as 
anger,  fear,  and  worry,  seriously  affect  the  digestive  system.  They 
cause  a  partial  paralysis  of  the  nerve  structures  that  control  the 
'digestive  organs,  and  make  good  digestion  impossible. 

403.  The  Nervous  System  as  a  Whole. —  If  we  could 
remove  all  the  remainder  of  the  body:  muscles,  bones,  and 
organs,  leaving  only  the  nerve  structures,  we  should  have 
a  " nerve  skeleton,"  which  would  preserve  the  general 
•outline  of  the  body.  This  is  another  way  of  saying  that 
*' nerves"  go  to  all  parts  of  the  body.  How  are  the 
" nerve  connections"  made  that  put  an  organ  (the  foot, 
for  example)  into  communication  with  the  brain?  We 
might  guess  at  the  answer,  and  say  that  the  nerve  fibers 
(axons)  are  fastened  together,  much  as  pieces  of  rope  are 
spliced,  or  as  wires  are  soldered  together.  But  this  does 
not  seem  to  be  true.  So  far  as  we  know,  there  is  no 
actual  joining  (or  at  most  only  a  slight  joining)  of  the 
neurons.  The  axon  has,  at  the  end  farthest  from  the 
<?ell  body,  a  number  of  short  branches,  called  the  end 


THE  NERVOUS  SYSTEM  AS  A  WHOLE  403 

brush.  By  the  interlacing  of  the  end  brush  of  one 
neuron  with  the  dendrite  of  another  neuron  there  is 
formed  a  conduction  pathway  for  the  nerve  impulse.  We 
can  compare  the  interlacing  of  end  brush  and  dendrite 
with  the  interlacing  produced  when  we  put  the  fingers  of 
the  one  hand  loosely  between  the  fingers  of  the  other. 

From  what  we  have  just  read  we  can  understand  that 
the  nerve  pathway,  along  which  an  impulse  must  travel, 
does  not  act  like  a  continuous  "wire,"  but  like  a  wire 
with  "breaks"  in  it,  or,  at  least,  with  places  where  there 
is  a  great  deal  of  resistance  (cf.  §  157).  Because  there  are 
"breaks"  in  its  path,  some  of  them  harder  to  cross,  some 
easier,  the  nerve  impulse  finds  a  preferred  pathway. 
This  is  the  easiest  path:  the  "path  of  least  resistance." 
In  much  the  same  way  a  stream  of  water  flowing  over 
rocky  soil,  although  it  seems  to  have  many  courses  from 
which  it  can  choose  its  channel,  turns  aside  from  all  but 
the  one  that  offers  the  least  resistance.  We  can  also 
compare  the  nerve  impulse  to  a  traveller.  While  the 
traveller  is  inexperienced,  one  route  looks  as  good  as  an- 
other; but  when  he  has  travelled  many  times,  he  finds 
certain  "connections"  easy,  and  always  goes  by  the 
routes  that  give  those  connections. 

How  are  these  " preferred  pathways"  laid  out  for  our  nerve  im- 
pulses? Some  of  them  we  inherit:  the  same  impulses  came  to  our 
ancestors,  and  found  the  " paths  of  least  resistance"  long,  long  ago. 
But  others  of  these  pathways  are  developed  by  experience.  As  some 
certain  stimulus  moves  again  and  again  through  the  same  chain  of 
neurons,  it  finds  the  path  easier  and  easier  to  follow,  until  it  finally 
falls  into  that  path,  automatically,  as  soon  as  it  starts  on  its  journey 
to  or  from  the  central  system. 


404  THE  NERVES  AND  THE  SENSE  ORGANS 

The  student  may  wonder  how  the  afferent  impulse  that  comes  to  the 
central  system  can  be  "switched  over"  into  the  efferent  neurons,  and 
sent  back  to  the  organs.  The  making  of  this  connection  is  the  work  of 
the  associating  neurons.  If  the  proper  associating  neurons  are  in  the 
spinal  cord,  then  the  impulse  will  go  no  higher  than  the  cord;  it  will  be 
turned  over,  at  once,  to  the  efferent  neurons.  For  certain  impulses 
the  associating  neurons  are  in  the  bulb ;  for  others  they  are  only  in  the 
cerebrum. 

404.  Voluntary    Action. —  We    have    already    learned 
(cf.  §§  355  and  398)  that  the  organs  of  the  body  are  moved 
by  muscles,  and  that  some  muscles  are  under  the  control 
of  the  will  (voluntary  muscles),  while  other  muscles  are 
involuntary,    carrying   out   their  functions   whether  we 
want  them  to    or   not.     All  the  muscular  action  that 
comes  from  the  use  of  the  will  gets  its  impulse  in  the 
cerebrum  (cf.  §  400).     If  we  see  a  pencil  lying  on  the 
floor,  the  sight  of  the  pencil  acts  as  a  stimulus  to  the 
cerebrum  and  to  the  mind.     If  we  want  the  pencil,  the 
cerebrum  sends  the  proper  impulses  to  the  muscles;  we 
stoop,  and  pick  up  the  pencil.     But  it  is  not  necessary  for 
us  to  pick  up  the  pencil  at  all;  we  may  prefer  to  step  upon 
it  instead.     Thus  the  mind  has  the  power  of  choosing 
what  stimuli  it  will  send  back  to  the  muscles. 

405.  Reflex  Action. —  Reflex  actions  are  involuntary 
actions.     They    are    called    reflex,    meaning    "bent    (or 
turned)  back,"  because  the  afferent  impulses  that  start 
them  are  turned  back  as  efferent  impulses.     If  the  asso- 
ciating neurons  are  below  the  cerebrum,   we  are  not 
conscious  of  either  the  stimulus  or  the  response  of  the 
organ  (cf.  §  403).     Of  this  sort  of  reflex  actions  are  the 
movements  of  the  internal  organs,  such  as  the  stomach, 


HABIT  405 

heart,  etc.  These  organs  send  word  of  their  wants  to  the 
central  nervous  system,  and  get  back  the  efferent  im- 
pulse, without  our  knowing  or  willing  anything  about  the 
operation.  Only  when  the  organs  are  injured  do  the 
impulses  which  they  send  get  to  the  cerebrum,  so  that 
we  feel  pain.  This  " sensation  of  injury"  gets  past  the 
lower  part  of  the  central  system  because  it  is  unusual; 
there  are  no  associating  neurons  to  turn  it  back  until  it 
reaches  the  cerebrum. 

But  it  is  not  only  our  internal  organs  that  act  reflexive- 
ly;  many  of  our  external  movements  are  not  voluntary. 
Thus,  the  blinking  of  the  eyelids,  which  is  for  the  pur- 
pose of  cleaning  and  moistening  the  eyeballs,  is  invol- 
untary. If  it  were  voluntary,  we  might  forget  to  do  it. 
When  you  put  your  hand  against  a  hot  stove,  you  jerk 
away  the  hand  before  you  feel  the  pain.  The  "jerking 
away"  is  a  reflex  act.  It  is  so  important  for  your  body 
that  your  hand  shall  not  be  burned,  that  a  part  of  the 
afferent  impulse  is  switched  over  into  the  efferent  chan- 
nels without  going  to  the  cerebrum.  But  it  is  necessary 
for  your  mind  to  know  that  hot  stoves  burn  your  hand,  so 
the  message  is  also  sent  to  the  cerebrum,  and  becomes  a 
part  of  your  memory. 

406.  Habit. —  Why  is  it  that  the  control  of  so  much 
that  the  body  does  is  left  to  involuntary,  reflex  action? 
We  can  understand  some  of  the  reasons  very  readily. 
In  the  first  place,  reflex  action  relieves  the  cerebrum  and 
the  mind  of  a  great  deal  of  work.  Then,  by  being  freed 
from  the  duty  of  controlling  the  internal  organs,  the 
cerebrum  has  time  to  do  a  much  higher  kind  of  work  for 


406       THE  NERVES  AND  THE  SENSE  ORGANS 

the  body.  It  can  be  used  for  getting  new  impressions; 
we  can  learn,  and  we  can  think.  Memory  belongs  to  the 
cerebrum  alone.  But  the  work  of  getting  new  impressions 
is  very  taxing  to  the  cerebrum,  so  there  is  a  device  for 
saving  work  here  also.  If  we  voluntarily  perform  a 
certain  act  again  and  again,  our  memory  becomes  more 
and  more  definite  regarding  the  act,  and  the  brain  needs 
to  make  less  and  less  effort  to  have  it  repeated.  So  we 
finally  acquire  the  power  of  reflex  action  in  doing  a  thing 
that  was  at  first  entirely  voluntary.  Such  acts  are  called 
acquired  reflex  acts,  to  distinguish  them  from  reflex  acts 
that  are  natural  to  us.  We  call  acquired  reflex  acts 
habits. 

The  power  of  forming  habits  is  a  great  economy  for  the  mind,  for 
the  reason  that  the  nervous  effort  required  in  the  learning  of  a  new 
trick  or  trade,  or  in  controlling  our  tempers,  is  too  great  to  be  kept 
up  always.  So  the  mind,  using  its  power  of  choice,  directs  the  cere- 
brum again  and  again  to  make  the  proper  "connections"  until  the  act 
becomes  reflex.  After  that  time  the  mind  depends  on  the  acquired 
" conduction  pathways"  to  carry  the  correct  impulses  to  the  muscles. 

While  nature  makes  a  good  act  easier  and  easier  to  perform,  it  visits 
its  punishment  upon  us  if  we  perform  bad  acts,  for  they  become  easier 
and  easier,  too.  Finally,  a  bad  act,  which  we  performed  at  first  only 
by  making  a  conscious  effort,  and  which  filled  us  with  shame  and 
disgust,  becomes  a  masterful  evil  habit  that  we  find  very  hard  to 
break.  We  need  to  keep  up  our  power  of  forming  habits,  and  to  use 
that  power,  deliberately,  to  form  good  habits,  so  that  it  will  be  easier 
and  easier  for  us  to  do  right,  and  harder  and  harder  to  do  wrong. 

407.  Effects  of  Alcohol  and  Tobacco  on  the  Nervous 
System. —  We  have  already  learned  some  of  the  effects  of 
alcohol  and  tobacco  (cf.  §§  371  and  391).  Alcohol  inter- 
feres with  digestion,  injures  the  liver  and  kidneys,  and 


EFFECTS  OF  ALCOHOL  AND  TOBACCO  407 

prevents  the  removal  of  body  waste.  It  makes  the 
drinker  liable  to  lung  diseases,  such  as  consumption  and 
pneumonia.  Because  of  these  facts  insurance  companies 
do  not  insure  the  lives  of  heavy  drinkers  at  all.  In 
making  out  its  rates,  and  the  conditions  under  which  it 
will  insure  persons,  an  insurance  company  does  not  deal 
with  a  few  individuals,  but  with  thousands  of  cases.  You 
may  know  a  man  who  has  drunk  whisky,  and  lived  to  old 
age.  His  case,  by  itself,  proves  nothing.  But  the  in- 
surance companies  have  kept  records,  now,  for  more  than 
half  a  century,  and  they  know  how  alcohol  affects  men. 
Their  verdict  is  that  the  death  rate  among  drinkers,  even 
moderate  drinkers,  is  from  25  to  40  per  cent  higher  than 
among  men  who  do  not  use  alcohol. 

Alcohol  works  injury,  not  only  to  certain  organs,  such 
as  those  of  digestion,  but  it  attacks  the  whole  body;  it 
does  so  through  the  most  delicate  organs  of  the  body: 
those  of  the  nervous  system.  Alcohol  injures  the  nerve 
cells;  in  the  steady  drinker  it  causes  them  to  break  down, 
and  to  become  useless.  Muscles  that  were  under  control 
become  uncertain,  and  the  hands  tremble.  The  user 
of  alcohol  takes  a  drink  to  " steady"  his  nerves,  but  he 
can  steady  them  for  only  a  little  time.  He  thus  develops 
a  habit  that  requires  the  constant  use  of  alcohol,  and  the 
alcohol  injures  his  body  more  and  more.  In  losing  their 
self  control  with  regard  to  alcohol,  many  drinkers  lose 
their  honesty  and  their  abhorrence  of  crime.  It  has  been 
found  true  again  and  again  that  criminals  drink  strong 
liquor  to  nerve  themselves  for  horrible  acts. 

People  sometimes  say  that  the  drinker  injures  only 
himself,  but  this  is  not  true.  His  friends  and  his  family 


408       THE  NERVES  AND  THE  SENSE  ORGANS 

suffer  with  him,  and  he  swells  the  numbers  of  the  insane 
and  dependent  —  people  for  whom  society  has  to  care, 
but  who  can  give  back  nothing  in  return. 

We  have  already  learned  that  the  cigarette  injures 
the  organs  of  respiration;  its  effect  is  much  worse  upon  the 
nervous  system,  especially  upon  that  of  young  people. 
Our  nervous  system  must  develop  with  our  years.  As 
we  acquire  skill,  new  nerve  structures  are  developed,  both 
in  the  organs  and  in  the  central  system.  The  nerve  cells 
of  the  boy  who  uses  cigarettes  do  not  grow  properly,  and 
the  chances  are  against  his  "making  good.'7  Instead  of 
becoming  alert  and  ready,  he  is  more  likely  to  lose  ground, 
and  to  become  backward  and  indifferent.  Only  a  small 
per  cent  (less  than  7)  of  the  school  children  who  smoke  are 
able  to  keep  up  their  work.  How  can  such  children  ex- 
pect, later,  to  satisfy  their  employers  or  customers,  and 
to  make  a  good  living?  It  is  not  for  nothing  that  the  best 
athletic  trainers  refuse  to  let  athletes  use  tobacco.  An 
athlete  needs  steady  nerves,  "wind,"  strength,  and  the 
ability  to  decide  quickly;  if  he  wishes  to  develop  these 
qualities  to  their  fullest  extent,  he  should  let  tobacco 
alone. 

408.  Exercises. 

1.  What  advantage  does  the  body  derive  from  a  central  nervous 
system?    What  advantage  does  a  telephone  system  derive  from  a 
central  station?    Is  there  any  disadvantage  in  either  case? 

2.  Give  other  illustrations,  besides  the  one  given  in  §  404,  of  the 
fact  that  the  mind  can  choose  what  stimuli  it  will  send  back  to  the 
muscles. 

3.  How  do  you  account  for  the  fact  that  you  can  recall  a  "for- 
gotten" event  by  a  hard  effort  of  the  memory? 


THE  SPECIAL  SENSES  9       409 

4.  A  foreigner  who  speaks  our  language  perfectly  when  at  ease 
often  falls  into  his  native  speech  when  excited.     Tell  why. 

5.  Why  is  the  order  for  the  closing  of  the  eyelids,  when  we  fear  an 
accident,  not  left  to  the  cerebrum? 

6.  If  the  cerebrum  of  a  person  were  removed,  and  he  lived,  could 
any  of  his  functions  go  on?    What  ones  could  not? 

7.  Why  is  the  idea  of  goodness  connected  in  our  minds  with  clean- 
ness? 

8.  How  does  a  baby  learn  to  speak  with  a  rough  voice,  or  with  a 
pleasant  one?  How  does  it  learn  to  speak  one  language  rather  than 
another? 

9.  Name  several  reflex  actions  of  the  external  organs. 

10.  Suppose  that  you  have  a  bad  temper;  in  the  light  of  what  you 
have  learned  about  habit,  suggest  how  you  could  get  control  of  your 
temper.    What  would  you  suggest  to  a  person  who  always  ' '  answers 
back,"  as  a  way  to  cure  himself  of  the  habit?    To  one  who  uses 
cigarettes? 

11.  Why  does  your  mouth  water  when  you  smell  a  good  dinner? 
How  do  the  salivary  glands  know  when  to  secrete  the  saliva?     Does  the 
11  watering"  of  the  mouth  serve  any  good  purpose? 

12.  How  are  nerve  impulses  started,  and  to  what  organ  are  they 
carried,  when  you  "read  over"  your  lesson  for  the  first  time?    What 
has  occurred  when  you  can  recite  it  perfectly? 

13.  Why  ought  the  performing  of  experiments  with  hydrogen,  in 
the  laboratory,  to  help  you  get  a  better  idea  of  this  gas  than  merely 
reading  about  it?    Give  the  reasons. 

409.  The  Special  Senses. —  By  the  special  senses  we 
mean  touch,  taste,  smell,  hearing,  and  sight.  The  organs 
of  the  special  senses  are  the  skin,  the  mouth  and  tongue, 
the  nose,  the  ears,  and  the  eyes.  Each  of  these  contains 
afferent  neurons  that  carry  to  the  brain  special  messages 
from  the  outside  world.  The  eyes  send  light  impulses, 
the  ears,  sound  impulses,  the  finger  tips,  feeling  impulses. 
As  these  impulses  come  to  the  brain,  we,  that  is,  our 


410 


THE  NERVES  AND  THE  SENSE  ORGANS 


minds,  must  interpret  them:  we  must  know  by  our  judg- 
ment and  our  "common  sense"  what  the  impulses  mean. 
We  say  that  the  messages  that  come  to  the  brain  produce 
sensations  in  the  mind.  The  ability  to  interpret  the 
messages  correctly  comes  to  the  mind  through  experience. 
When  the  neurons  in  the  finger  carry  to  the  brain  an  im- 
pulse that  is  started  by  a  needle  point,  the  mind  has  the 
sensation  of  touch,  or  of  pain.  The  usual  impulses  sent 
to  the  brain  from  the  stomach  produce  in  the  mind  the 
sensation  of  hunger;  the  usual  impulses  sent  by  the 
throat  produce  the  sensation  of  thirst.  We  call  the  sensa- 
tions that  come  from  impulses  within  the  body,  general 
sensations;  those  coming  from  im- 
pulses outside  of  the  body,  we  call 
special  sensations. 


Tactile 
Corpuscle 


Fig.  296. 
A  Touch  Corpuscle. 


410.  Touch. —  In  the  skin,  and  in 
the  mucous  membrane  of  the  tongue, 
are  little  elevations  ("papillae";  cf. 
§  392)  that  contain  the  touch  corpus- 
cles (Fig.  296).  Inside  the  touch  cor- 
puscles are  the  ends  of  the  nerve 
fibers.  When  we  touch  an  object,  the 
changes  in  the  pressure  against  the 
touch  corpuscles  set  up  impulses  in  the  nerve  fibers.  We 
feel  the  object  as  smooth  or  rough,  large  or  small,  sharp 
or  blunt,  hot  or  cold,  hard  or  soft,  according  to  the 
account  which  the  afferent  neurons  send  to  the  brain. 

The  sense  of  touch  is  not  equally  good  everywhere,  as  we  well  know. 
Its  acuteness  depends  on  the  number  of  touch  corpuscles  in  a  given 
area.  We  can  measure  its  acuteness  by  means  of  the  tips  of  a  pair  of 


TASTE 


411 


dividers,  or  by  two  pins.  The  tongue  can  feel  that  there  are  two 
points  when  they  are  only  x/25  of  an  inch  apart;  the  finger  tips,  when 
they  are  about  1/i2  of  an  inch  apart.  The  back,  however,  feels  the  two 
points  as  one,  even  when  they  are  I1/ '2  or  2  inches  apart. 

The  sense  of  temperature  is  also  in  the  skin  and  mucous  mem- 
brane. A  chemist,  in  trying  to  find  out  whether  a  reaction  causes  a 
rise  of  temperature,  often  holds  to  his  lips  the  vessel  with  which  he  is 
working,  because  the  lips  are  especially  sensitive  to  heat  and  cold. 

411.  Taste. —  The  nerves  of  taste  end  in  the  mucous 
membrane  of  the  tongue  and  the  back  of  the  mouth 
(Fig.  297).  Only  liquids  and  dissolved  substances  can 
be  tasted  (cf.  §  359);  solids 
cannot  get  to  the  afferent 
taste  neurons.  Some  parts 
of  the  tongue  are  much  more 
sensitive  to  taste  than  others, 
and  different  parts  of  the 
tongue  recognize  different 
tastes.  -  There  are  sweet  and 
bitter  tastes,  sour  and  salty 
tastes,  and  combinations  of 
these.  Some  of  the  nerves 
of  taste  end  in  special  struc- 
tures  called  taste  buds.  The  Tongue, 
The  "buds"  contain  little 
cavities  that  open  into  the  mouth;  in  the  openings  of  the 
cavities  the  "taste  cells"  come  into  very  close  contact 
with  the  food  solution. 

The  sense  of  taste  can  be  greatly  developed  by  use.  Professional 
"tasters"  of  tea,  coffee,  foods,  etc.,  become  very  skillful.  A  good 
sense  of  taste  is  a  valuable  protection  to  us,  for  it  enables  us  to  judge 


412 


THE  NERVES  AND  THE  SENSE  ORGANS 


of  the  quality  of  food  before  we  swallow  it.  What  we  call  the  ' '  taste  " 
of  a  substance  is  often  a  combination  of  smell  and  taste.  Some  of  the 
"strong"  brands  of  cheese,  for  example,  have  a  mild  taste  if  we  hold 
our  noses  while  eating  them. 

412.  Smell. —  The  sense  of  smell,  like  the  sense  of 
taste,  is  at  the  opening  of  the  alimentary  canal.  But  the 
sense  of  smell  guards  our  organs  of 
respiration  as  well  as  those  of  digestion, 
for  it  passes  upon  the  good  or  bad 
quality  of  the  air  we  breathe.  Smell 
can  recognize  only  gaseous  substances, 
and  not  all  of  those.  Thus,  air, 
oxygen,  and  hydrogen  are  odorless. 
The  neurons  that  send  odor  impulses 
to  the  brain  end  at  the  olfactory  cells ; 
these  are  in  the  upper  part  of  the  nose 
cavity  (Fig.  298). 


Fig.  298. 

Sense     of    Smell;     the 
Olfactory  Cells. 


Wild  animals  and  primitive  men  have  an 
acute  sense  of  smell,  and  can  easily  recognize 
odors  at  some  distance,  but  civilized  man  usually 
has  the  sense  in  only  a  blunted  form.  For  him 
all  odors  are  classified  as  pleasant  or  unpleasant,  and  he  does  not 
distinguish  them  further.  The  trained  scientist  often  develops  his 
sense  of  smell  to  a  high  degree,  so  that  he  is  able  to  recognize  sub- 
stances by  their  odors  even  when  very  small  amounts  of  the 
substances  are  present. 

413.  Hearing;  Structure  of  the  Ear. —  We  have  already 
learned  that  sound  is  due  to  the  vibrations  of  some  body 
(cf.  §  189),  and  that  the  vibrating  body  sets  up  sound 
waves  in  the  air.  The  ear  (Fig.  299)  is  the  organ  of 
hearing;  in  it  are  the  afferent  neurons  that  respond  to 


HEARING;  STRUCTURE  OF  THE  EAR 


413 


sound  waves.  The  ear  is  usually  considered  under  its 
three  divisions:  (1)  the  outer  ear;  (2)  the  middle  ear; 
(3)  the  inner  ear. 

The  outer  ear  is  a  funnel-shaped  structure  made 
of  cartilage  and  skin;  it  is  used  for  the  purpose  of 
collecting  sound  waves.  The  tube  that  leads  to  the 
middle  ear  is  called  the  auditory  canal. 


Cochlea 


Eustachian 
Tube 
•H/^" 
Fig.  299. 
Structure  of  the  Ear;  Section  through  the  Temporal  Bone. 

The  middle  ear  is  a  hollow  in  the  temporal  bone 
(cf.  Fig.  275,  §  354) ;  it  is  called  the  ear  drum,  or 
tympanum.  Between  the  middle  ear  and  the  auditory 
canal  is  stretched  the  membrane  (tympanic  membrane) 
which  corresponds  to  the  "drum  head."  A  chain  of  3 
small,  connecting  bones  (cf.  §  354)  stretches  across  the 
middle  ear.  The  first  of  them  is  attached  to  the 
tympanic  membrane,  and  the  last  reaches  to  the  opening 
of  the  inner  ear.  The  middle  ear  is  connected  with 


414       THE  NERVES  AND  THE  SENSE  ORGANS 

the  pharynx,  or  throat  (c/.  §  361)  by  the  Eustachian 
(u-stak'-e-an)  tube.  This  tube  allows  the  air  to  press  on 
the  inside  of  the  tympanic  membrane,  and  to  balance  the 
pressure  of  the  air  in  the  auditory  canal.  Otherwise  a 
sudden  change  in  the  outside  air  pressure  might  burst 
the  tympanic  membrane.  When  cannon  are  being  fired, 
persons  standing  near  are  instructed  to  hold  their 
mouths  open,  so  that  the  air  sjiock  on  the  inner  side  of 
the  membrane  may  be  equal  to  that  on  the  outer  side. 

The  outer  ear  gathers  the  sound  waves,  and  the  middle 
ear  passes  the  vibrations  on  to  the  inner  ear,  the  real 
organ  of  hearing.  The  inner  ear  is  filled  with  liquids. 
It  is  separated  from  the  middle  ear  by  a  membrane;  to 
this  membrane  the  last  bone  of  the  middle  ear  is  attached. 
As  the  membrane  is  made  to  vibrate,  it  gives  its  motion 
to  the  liquids  of  the  inner  ear.  The  vestibule  is  the 
first  chamber  of  the  inner  ear.  The  cochlea  (k5k'-le-a) 
is  like  a  snail  shell,  and  this  fact  gave  it  its  name.  It  is 
the  part  of  the  ear  that  contains  the  fibers  of  the  auditory 
nerve. 

Besides  the  cochlea  and  vestibule,  the  inner  ear  contains  the  semi- 
circular canals.  These  are  not  part  of  the  hearing  apparatus,  but 
they  are  probably  organs  that  tell  the  brain  in  what  direction  the  body 
is  leaning,  and  so  help  in  keeping  the  body  balanced. 

The  ears  should  be  cared  for  intelligently.  Sharp  objects  should 
not  be  put  into  them,  and  they  should  never  be  pulled  or  "boxed,"  for 
fear  that  the  "drum  head"  may  be  burst.  The  earwax  is  intended 
to  keep  insects  out  of  the  ear,  and  should  not  ordinarily  be  removed 
until  it  comes  out  of  the  auditory  canal.  Clean  warm  water  will 
remove  earwax  better  than  anything  else.  An  unusually  large  secre- 
tion of  earwax  sometimes  causes  dull  hearing  and  deafness,  but  no  one 
except  a  physician  ought  to  try  to  remedy  the  trouble. 


EYE  SOCKETS  AND  LIDS  415 

414.  Sight. —  Light  is  the  cause,  or  stimulus,  outside 
of  us  that  produces  the  sensation  of  sight,  or  seeing 
(cf.  §  167).    The  eye  is  the  organ  that  is  sensitive  to  the 
light  waves  that  come  to  us.     But  the  eye  is  not  merely  a 
"light  spot,"  an  organ  to  distinguish  light  from  darkness. 
It  is  a  structure  that  enables  us  to  perceive  light  that  has 
been  changed  by  objects  that  reflect  it,  or  refract,  trans- 
mit, or  partly  absorb  it,  so  that  we  see  the  illuminated 
objects  in  all  their  variety  of  light  and  shade,  form  and 
color.     The  eye  collects  these  modified  light  waves,  bends 
them  so  that  they  come  to  a  focus,  and  out  of  them  forms 
an  image  on  the  retina  (cf.  §  416). 

415.  Eye  Sockets  and  Lids. —  The  eye  is  admirably 
protected.     It  is  set  into  sockets  in  bones  of  the  skull,  so 
that  it  is  shielded  on  all  sides  except  in  front.     The 
sockets  are  lined  with  fatty  tissue  covered  by  a  double 
membrane.     The  fat  and  membrane  not  only  make  the 
socket  smooth,  but  they  also  form  a  soft  cushion  for  the 
eye  ball,  in  case  it  is  forced  inward  by  a  blow. 

The  eye  is  protected  in  front  by  the  eyebrow,  the  eye- 
lashes, and  the  eyelids.  The  bone  forming  the  brow  pro- 
jects over  the  eye  like  a  roof,  protecting  it  against  blows 
from  above.  At  the  same  time  the  hairs  of  the  eyebrow 
act  like  eaves  troughs,  and  drain  off  perspiration,  so  that 
it  does  not  run  down  into  the  eye.  The  eyelashes  shade 
the  eye  from  "high  light,"  and  keep  out  dust.  The 
eyelids  move  with  incredible  speed  when  the  eye  is  in 
danger  (cf.  §  405),  so  that  the  "twinkling  of  an  eye"  is 
really  a  very  short  space  of  time.  Experimenters  have 
again  and  again  owed  the  preservation  of  their  eye- 


416 


THE  NERVES  AND  THE  SENSE  ORGANS 


Sclerotic 
Coat 


sight  to  the  fact  that  reflex  action  closed  their  eyelids 
before  the  pieces  scattered  by  an  explosion  could  travel 
to  the  eye. 

The  eyelids  are  lined  with  a  very  sensitive  membrane, 
the  conjunctiva.  The  same  membrane  covers  the  front 
of  the  eyeball.  When  we  get  a  cinder  into  one  of  our 
eyes,  and  it  hurts  badly,  we  ought  to  remember  that 
the  pain  is  the  conjunctiva's  way  of  telling  us  that 
the  eye  is  in  danger,  and  that  we  must  remove  the  tres- 
passing cinder. 

•  .  -- 

416.  Parts  of  the  Eye. —  In  many  respects  the  eye  is 
like  a  camera  (cf.  §  188).  It  contains  a  lens,  called  the 

crystalline  lens 
(Fig.  300),  a 
"shutter,"  called 
the  iris,  for  regu- 
lating the  amount 
of  light  that  can 
get  into  the  eye, 
a  sensitive  mem- 
brane, the  retina, 
for  receiving  the 
image,  and  an  ar- 
rangement, called 
accommodation, 
which  changes 
the  focusing  as  objects  are  near  or  distant. 

The  crystalline  lens  divides  the  eye  into  two  chambers 
of  unequal  size.  The  smaller  one  is  in  front,  and  con- 
tains a  liquid  called  the  aqueous  (or  "watery")  humor. 


Optic 
Nerve 


Fig.  300. 
Parts  of  the  Eye. 


PARTS  OF  THE  EYE  417 

The  larger  chamber  is  filled  with  a  jelly-like  liquid  called 
the  vitreous  (or  "glassy")  humor.  These  two  humors 
keep  the  eye  round  and  full.  They  and  the  crystalline 
lens  together  make  up  a  double-convex  lens  (cf.  §  178), 
and  throw  on  the  retina  an  inverted  image  of  the  object 
seen. 

The  outside  coating  of  the  eyeball  is  tough  and  strong; 
it  is  called  the  sclerotic  (skler-ot'-ic)  coat.  It  is  opaque 
everywhere  except  in  front,  where  it  becomes  trans- 
parent, and  is  called  the  cornea.  The  "white  of  the  eye" 
is  the  visible  part  of  the  sclerotic  coat.  The  choroid 
(ko'-roid)  coat  is  inside  of  the  sclerotic  coat.  It  is  dark  in 
color,  and  acts  like  the  dark  interior  of  a  camera:  it 
absorbs  light,  and  so  prevents  the  light  from  being 
reflected  back  and  forth  inside  the  eye.  The  iris  is  a  part 
of  the  choroid  coat;  it  acts  as  a  curtain  for  the  eye,  and 
gives  the  eye  its  color.  The  pupil  is  an  opening  in  the 
center  of  the  iris.  It  is  controlled  by  two  sets  of  muscles, 
which  open  or  close  it,  according  to  the  amount  of  light. 
In  the  cat  the  pupil  becomes  a  narrow  slit,  when  the  light 
is  bright. 

The  retina  (ret'-i-na)  is  the  innermost  coat  of  the 
eye;  it  covers  the  back  portion  of  the  choroid  coat.  The 
retina  is  very  complex.  By  a  delicate  arrangement  of 
cells  it  arouses  afferent  light  impulses  in  the  neurons  of 
the  optic  nerve.  The  blind  spot  of  the  eye  is  the  place 
where  the  optic  nerve  begins  to  spread  out  to  form  the 
retina. 

The  eyeball  is  held  in  place,  and  moved  about,  by  means  of  6  small 
muscles.  The  transparent,  front  portion  of  the  eye  must  be  kept  moist 
and  clean,  hence  the  eye  has  lachrymal  (lak'-rf-mal),  or  "tear," 


418 


THE  NERVES  AND  THE  SENSE  ORGANS 


glands  (Fig.  301).    These  secrete  tears,  and  pour  them  over  the  eyes. 
The  tear  glands  are  in  the  upper,  outer  corners  of  the  eyes.    Their 
secretions  are  carried  by  a  duct,  or  tube,  into  the  nostrils.    When  the 
tears  are  secreted  in  larger  amounts  than 
the  ducts  can  carry  off,  we  "cry":  the  tears 
overflow  the  lids. 


Lachrymal 
Gland 


Nasal 
Cavity 


Fig.  301. 

Relation  of  a  Lachrymal 
Gland  to  the  Eye. 


417.  Accommodation. —  The  crys- 
talline lens  and  cornea  together  form 
the  most  important  focusing  part 
of  the  eye.  The  crystalline  lens 
differs  from  a  glass  lens  in  that  it 
is  very  elastic;  if  left  to  itself,  it 
becomes  more  convex.  On  this  fact 
accommodation  depends.  The  lens 
is  held  to  the  choroid  coat  by  a  ligament  called  the  sus- 
pensory ligament.  Ordinarily  this  ligament  is  stretched 
tight  by  the  choroid  coat,  and  flattens  the  lens.  When  the 
lens  needs  to  be  more  rounded,  the  ciliary  muscles,  which 
are  attached  to  the  sclerotic  coat,  draw  the  choroid  coat 
forward.  The  result  is  that  the  suspensory  ligament  is 
loosened,  and  the  lens  is  allowed  to  become  more  convex. 
This  power  of  the  eye  to  change  the  curvature  of  the  lens 
is  accommodation. 


The  need  for  accommodation  is  plain  if  we  know  the  properties  of 
light.  When  light  from  a  distant  object,  such  as  a  tree,  comes  to  us, 
the  light  rays  are  almost  parallel;  hence  the  lens,  though  flattened,  can 
bring  the  light  to  a  focus  on  the  retina  (cf.  Fig.  153,  §  178).  But  when 
you  look  at  a  near  object,  the  light  rays  from  any  point  of  the  object 
spread  out,  and  make  a  large  angle  with  one  another;  hence  a  lens 
with  a  more  rounded  surface  is  needed  to  bring  the  rays  to  a  focus. 
As  we  become  older,  the  crystalline  lens  loses  its  elasticity,  and  does 


NEAR-  AND  FAR-SIGHT 


419 


not  become  rounded  when  it 
is  released.  We  are,  therefore, 
likely  to  lose  the  power  of  accom- 
modation. 

418.  Near-  and  Far-Sight; 
Care  of  the  Eyes. —  When  a 
normal  eye  is  at  rest,  it  is 
in  focus  for  distant  objects. 
For  close  objects,  accommo- 
dation must  be  used.  A 
"  near-sighted  "  eye  (Fig. 
302)  cannot  see  objects  dis- 
tinctly at  more  than  about 
10  inches'  distance;  when 
the  object  is  at  a  greater 
distance,  the  focus  is  formed 
in  front  of  the  retina.  Hence 
the  light  rays  have  crossed 
before  reaching  the  retina, 
and  the  image  is  blurred. 
The  remedy  for  short- 
sightedness is  a  concave  lens 
(cf.  §  178)  of  the  right  cur- 
vature. This  throws  the 
image  farther  back,  upon  the 
retina. 

In  far-sighted  vision  the 
object  to  be  seen  must  be 
more  than  10  inches  away; 
otherwise  the  image  will  fall 
behind  the  retina.  Of  course 


Fig.  302. 

Diagram  of  a  Normal  Eye,  a  Near- 
Sighted  Eye,  and  a  Far-Sighted  Eye. 
The  near-sighted  eye  needs  a  concave 
lens;  the  far-sighted  eye,  a  convex  lens. 
The  dotted  curved  lines  show  where  the 
retina  would  be,  if  the  defective  eye  were 
normal.  The  dotted  straight  lines  show 
how  the  light  rays  are  brought  to  a 
focus  by  the  proper  eye-glasses. 


420  THE  NERVES  AND  THE  SENSE  ORGANS 

this  is  impossible,  since  the  retina  is  opaque;  but  the 
image  on  the  retina  is  blurred,  because  the  light  is  not 
yet  at  a  focus.  The  crystalline  lens  prevents  far-sight, 
if  it  has  the  power  of  accommodation.  When  this 
power  is  gone,  convex  lenses  are  needed  to  help  the 
crystalline  lens,  and  to  make  accommodation  unne- 
cessary. 

Astigmatism  (a-stfg'-mat-ism)  is  a  defect  of  vision  that  is  due  to  a 
lack  of  sufficient  curving,  or  a  flatness,  in  some  part  of  the  cornea  or 
crystalline  lens.  The  muscles  of  the  eye  keep  trying  to  adjust  the  eye 
and  the  lens  so  as  to  make  a  distinct  image,  and  become  worn  out  in 
the  attempt.  Glasses  for  astigmatic  eyes  are  made  to  correct  the 
particular  trouble  of  each  eye,  and  are  of  no  use  unless  an  expert 
oculist  fits  them.  There  are  few  errors  of  vision  that  the  oculist  cannot 
correct,  and  we  should  consult  him  at  once  if  we  have  any  difficulty 
with  our  eyesight.  Poor  vision  causes  a  constant  strain  upon  the 
eyes,  with  headaches,  inflammation  of  the  eyes,  and  nervousness. 
Wonderful  improvement  in  the  general  health  often  follows  the 
wearing  of  the  right  glasses,  and  the  relieving  of  the  eye  from  strain. 
The  eye  is  so  delicate  that  if  it  is  upset  the  whole  nervous  system 
feels  the  effect. 

Care  of  the  Eyes. —  We  should  never  rub  the  eyes  with 
the  fingers  unless  we  are  certain  that  the  fingers  are  clean ; 
otherwise  the  eyes  may  become  infected.  We  should 
read  only  in  a  good  light,  but  the  light  should  not  be  too 
bright,  and  should  not  be  reflected  directly  to  the  eye. 
Sunlight  is  too  bright  for  reading.  If  we  read  or  study  by 
lamplight,  either  our  eyes  or  the  lamp  should  be  shaded, 
best  by  a  green  shade.  We  ought  not  to  read  in  a  moving 
train  or  street  car  for  more  than  a  little  while.  The  jar- 
ring of  the  car  causes  the  book  to  shake,  and  the  eye  is 


SUMMARY  421 

strained  in  trying  to  follow  it.  We  ought  not  to  read 
while  lying  down;  the  position  is  awkward,  and  trying 
to  the  eyes. 


419.  Summary.—  The  body  is  one  organism.  The  nervous  sys- 
tem regulates  the  body  by  providing  communication  between  its  parts. 
The  nervous  system  consists  of  the  central  and  the  sympathetic 
systems. 

Neurons  are  nerve  cells.  They  consist  of  cell  bodies,  and  of 
nerve  fibers,  or  axons.  Dendrites  are  short  extensions  of  cell 
bodies. 

A  nerve  is  a  bundle  of  nerve  fibers.  A  nerve  message  is  called  a 
stimulus,  or  nerve  impulse.  Nerve  fibers  are  of  3  kinds:  afferent 
(sensory),  efferent  (motor),  and  associating. 

Groups  of  neurons  are  called  ganglia. 

The  brain  consists  of  forebrain,  midbrain,  and  hindbrain. 

The  cerebrum  is  the  forebrain.  It  communicates  with  the  body 
through  the  midbrain,  hindbrain,  and  spinal  cord,  but  it  has  also  direct 
connection,  by  means  of  cranial  nerves,  with  parts  of  the  head, 
neck,  and  trunk. 

The  cerebrum  is  the  organ  of  the  mind. 

The  hindbrain  consists  of  the  cerebellum,  pons,  and  bulb. 

The  spinal  cord  is  enclosed  in  the  spinal  column.  Its  out- 
side consists  of  white  nerve  fibers;  its  inside  of  gray  cell  bodies.  It 
has  many  pairs  of  nerves;  each  nerve  has  afferent  and  efferent 
fibers. 

The  sympathetic  system  consists  of  ganglia  and  nerve  fibers  that 
control  the  internal  organs  and  the  skin.  The  sympathetic  system 
relieves  the  central  system  of  much  labor,  but  it  cannot,  of  itself,  send 
back  efferent  impulses  to  the  organs. 

Nerve  connections  are  commonly  made  by  the  interlacing  of  the 
"end  brush"  of  a  nerve  fiber  with  the  dendrites  of  a  neighboring  cell 
body. 

The  conduction  pathway  taken  by  a  nerve  impulse  is  the  one  that 
offers  the  least  resistance. 


422  THE  NERVES  AND  THE  SENSE  ORGANS 

The  nerve  organ  to  which  an  afferent  impulse  must  go,  before  being 
returned  as  an  efferent  impulse,  depends  on  the  position  of  the  asso- 
ciating neurons  for  that  impulse. 

Voluntary  acts  are  directed  by  the  cerebrum. 

Reflex  acts  are  either  natural  or  acquired.  Acquired  reflex  acts  are 
habits.  Natural  reflex  acts  have  their  associating  neurons  in  organs 
below  the  cerebrum.  Habits  have  their  associating  neurons  in  the 
cerebrum,  but  as  parts  of  preferred  pathways,  so  that  the  turning 
back  of  the  impulse  in  the  right  direction  requires  little  or  no  effort 
of  the  mind. 

Alcohol  injures  the  whole  body  by  attacking  the  nerve  cells. 

Tobacco  prevents  the  nervous  system  from  developing  properly, 
and  is,  therefore,  very  injurious  to  young  people.  Cigarettes  are  worse 
than  ordinary  tobacco. 

The  special  senses  are  touch,  taste,  smell,  hearing,  and 
sight. 

Sensations  are  the  interpretations,  made  by  the  mind,  of  the  afferent 
impulses  that  come  to  the  brain.  There  are  general  and  special 
sensations. 

Touch  is  due  to  nerve  fibers  in  the  touch  corpuscles  of  the  skin.  It 
is  most  delicate  in  the  tongue  and  fingers. 

Taste  is  the  result  of  stimuli  received  by  certain  nerves  that  end 
in  the  mucous  membrane  of  the  tongue  and  mouth.  Only  substances 
in  solution  can  give  the  stimuli. 

Smell  is  due  to  impulses  aroused  in  certain  neurons  by  the  olfactory 
cells. 

Hearing  is  the  effect  of  sound  impulses  set  up  in  the  audi- 
tory nerve.  This  nerve  ends  in  the  cochlea,  a  part  of  the  inner 
ear. 

Sight  is  the  sensation  produced  by  light  stimuli  that  are  carried  to 
the  brain  from  the  retina. 

The  retina  is  the  outspread  end  of  the  optic  nerve. 

The  lachrymal  glands  secrete  tears  to  wash  the  eyeballs. 

Accommodation  is  the  power  of  the  eye  to  alter  the  curvature  of  the 
crystalline  lens,  so  that  light  from  both  near  and  distant  objects  may  be 
brought  to  a  focus  on  the  retina. 


EXERCISES  423 

In  near-sight  the  light  rays  are  brought  to  a  focus  too  far  in  front 
of  the  retina.  The  remedy  is  concave  glasses. 

In  far-sight  the  light  rays  are  not  brought  to  a  focus  at  all.  The 
focus  would  be  behind  the  retina,  if  this  were  possible.  The  remedy 
is  convex  glasses. 

The  eyes  should  not  be  strained  by  being  used  in  too  bright  a  light, 
too  dim  a  light,  or  in  awkward  positions.  If  defective,  they  should  be 
cared  for  by  a  competent  oculist. 

420.    Exercises. 

1.  Name  as  many  sensations  as  you  can,  and  tell  what  impulses 
produce  them. 

2.  "Saccharine"  is  a  white  solid  having  several  hundred  times  the 
sweetening  power  of  sugar.     A  tiny  amount,  placed  on  the  tongue,  is 
sweet;  a   larger   amount   is  intensely  bitter.     Can   you   suggest  a 
reason? 

3.  How  would  you  set  about  cultivating  your  sense  of  smell,  so 
as  to  make  it  acute?    What  do  you  think  would  happen  in  the 
olfactory  cells,  if  you  were  to  do  this?    In  the  brain? 

4.  Name  the  organs  through  which  a  sound  must  travel  before  it 
reaches  the  auditory  nerve. 

5.  Stand  before  a  mirror,  in  the  dark,  for  a  minute,  and  then  sud- 
denly turn  on  a  light;  what  is  the  condition  of  the  pupils  of  your  eyes? 
What  happens  as  the  light  shines  into  your  eyes?    Tell  why  we  are 
dazed  when  we  first  come  from  the  dark  into  a  bright  light.    Why  can 
we  not  see  so  well  when  we  first  go  into  a  dark  room  as  we  can  after  we 
have  been  in  it  for  a  time? 

6.  Name  all  the  structures  through  which  a  ray  of  light  must  go  to 
reach  the  optic  nerve. 

7.  Read  about  the  "compound"  eyes  of   insects,  and  describe 
them. 

8.  If  it  is  true  that  the  image  on  the  retina  is  inverted,  why  do  we 
not  see  objects  upside  down? 

9.  A  fly  held  near  the  eye  looks  as  large  as  a  man  who  is  down  the 
street;  how  do  we  know  it  is  not  really  as  large? 


424  THE  NERVES  AND  THE  SENSE  ORGANS 

10.  When  a  stick  with  a  spark  at  one  end  is  swung  about  in  a  circle, 
the  eye  "sees"  a  continuous  ring  of  light;  why?    Why  does  a  meteor 
(" shooting  star")  seem  to  have  a  "tail?" 

11.  Why  does  it  rest  the  eye,  after  we  have  been  reading,  to  look  at 
a  distant  object? 

12.  Adenoids,  colds  in  the  throat,  etc.,  often  cause  deafness;  what 
part  of  the  ear  do  they  stop  up  first? 


CHAPTER  XX 

SANITATION 

421.  Bacteria  and  Disease. — We  have  already  learned 
(cf.  §  324)  that  bacteria  are  plants  belonging  to  the  class 
of  fungi,  and  that  they  cause  many  fermentations,  the 
decay  of  dead  animals  and  plants,  and  diseases  that  are 
"catching,"  or  contagious.  All  disease  germs  are  not, 
however,  bacteria;  some  of  them  are  minute  one-celled 
animals  (protozoa).  Thus,  malaria  and  yellow  fever  are 
caused  by  protozoa.  It  is  impossible  for  us  to  escape 
from  germs,  for  they  are  everywhere  about  us:  on  the 
ground,  in  the  air,  and  in  our  houses;  but,  fortunately  for 
us,  all  germs  do  not  cause  disease.  Most  of  them  live 
their  own  lives  without  interfering  with  ours.  In  the 
outside  air  we  should  rarely  meet  with  injurious  germs 
were  it  not  that  they  escape  from  the  bodies  of  animals 
and  of  persons  who  are  sick.  So  the  germs  we  usually 
have  to  fear  are  those  that  are  carried,  in  food  or  by  con- 
tact, from  animals  to  persons,  or  from  one  person  to 
another. 

The  "germ  theory"  of  contagious  diseases  did  not  gain  immediate 
acceptance  when  it  was  first  stated,  for  men  could  not  believe  that 
organisms  so  small  could  do  so  much  mischief.  But  the  patient  labor 
of  one  investigator  after  another  proved  that  the  theory  is  correct. 
We  now  know  that  germs  are  responsible  for  smallpox,  measles, 
diphtheria,  scarlet  fever,  typhoid  fever,  tuberculosis,  influenza  (la 
grippe),  malaria,  yellow  fever,  pneumonia,  lockjaw  (tetanus),  mumps, 
cholera,  leprosy,  the  plague,  etc.,  etc.  It  takes  a  definite  kind  of  germ 

425 


426  SANITATION 

to  cause  a  given  disease;  no  other  germ  will  "do  just  as  well."  But  the 
ways  of  different  kinds  of  germs  are  not  at  all  alike;  it  is  often  very  hard 
for  the  investigator  to  know  just  how  each  kind  of  germ  gets  into  the 
body,  and  how  it  does  its  work.  Thus,  it  turns  out  that  while  a  cer- 
tain mosquito,  called  anopheles  (a-nof'-e-les) ,  carries  malaria  germs 
from  one  person  to  another,  only  the  female  anopheles  sucks  blood,  and 
is  responsible  for  the  spreading  of  malaria. 

The  science  of  germs,  and  of  the  way  in  which  we  can 
deal  with  them,  is  bacteriology.  The  science  of  keeping 
the  body  in  good  health  is  hygiene.  The  study  of  the 
conditions  and  surroundings  that  make  for  the  health  of 
the  body  and  of  the  community,  is  sanitation. 

422.  How  the  Body  Gets  and  Resists  Diseases. — 
Germs,  like  other  living  organisms,  grow  rapidly  when  the 
conditions  for  life  (environment;  cf.  §  306)  are  favorable. 
They  need  animal  or  vegetable  material  for  food;  they 
need  moisture;  they  need  a  favorable  temperature. 
Germs  often  find  these  conditions  in  our  solid  food,  in 
milk,  in  water  containing  organic  matter,  in  the  filth  of 
the  streets,  and  in  the  animals  that  make  their  home 
with  man.  These  animal  companions  of  man  are  ver- 
min, pets,  and  domestic  animals.  From  food,  and 
water,  and  animals,  then,  disease  germs  are  transferred 
to  man.  In  the  body  of  man  they  find  conditions  favor- 
able, and  thrive  enormously.  The  stomach  secretion 
kills  many,  but  certain  kinds  are  able  to  get  through  the 
stomach  (cf.  §  364).  Some  find  favorable  conditions  in 
the  warm,  moist  cells  of  the  throat  and  lungs;  others, 
still,  get  into  the  blood  through  cuts  and  scratches  in  the 
skin.  When  we  think  of  how  constantly  we  come  in  con- 


HOW  THE  BODY  GETS  AND  RESISTS  DISEASES        427 

tact  with  objects  that  contain  harmful  germs,  we  are  im- 
pressed with  at  least  3  things:  (1)  how  efficient  our  skin 
is  in  keeping  out  the  invading  army  of  germs;  (2)  how 
important  it  is  to  wash  the  skin,  especially  that  of  the 
hands,  so  that  we  may  remove  the  germs  before  they 
get  into  our  food;  (3)  how  necessary  it  is  to  keep  the  nasal 
passages  and  the  mouth  (including  the  teeth)  clean,  so 
that  germs  may  not  develop  there,  and  spread  disease  to 
the  other  parts  of  the  body. 

Why  do  not  the  germs  of  disease  destroy  man  at  once? 
The  answer  is  that  there  are  two  sides  to  the  battle;  the 
body  has  its  defenders,  as  well  as  its  enemies.  One  of 
these  is  the  army  of  white  corpuscles,  which  destroys 
many  of  the  disease  germs  that  get  into  the  blood.  We 
have  already  seen  (cf.  §  378)  that  the  white  corpuscles  are 
like  amebas,  and  that  they  are  not  only  in  the  blood,  but 
get  through  the  capillaries  into  the  lymph.  If  a  wound  is 
made  in  the  skin  or  mucous  membrane,  the  white  cor- 
puscles do  their  best  to  destroy  the  germs  that  enter  the 
wound.  The  body  has  not  only  the  white  corpuscles  to 
defend  it,  but  also  produces  certain  substances  that  act 
as  germicides  ("germ  slayers").  A  great  part  of  the 
reason  why  we  need  to  keep  the  body  rested,  well-fed,  and 
strong  is  that  it  may  have  an  abundance  of  vigorous  white 
corpuscles,  and  that  it  may  produce  the  right  germicides 
for  the  germs  that  attack  it.  Yet,  in  spite  of  everything 
that  the  body  can  do,  some  dangerous  bacteria  may  get 
past  the  body's  lines  of  fortifications;  we  then  have  a 
disease. 

The  effect  which  disease  germs  have  upon  the  body  is 
due  not  so  much  to  the  germs  themselves  as  to  the  sub- 


428  SANITATION 

stances  that  the  germs  produce.  These  substances  are 
violent  poisons,  called  toxins;  they  injure  the  cells  of  the 
body  much  as  strychnine  or  other  poisons  would.  Pto- 
maines (to'-ma-ins),  which  cause  so-called  ptomaine 
poisoning,  are  toxins  produced  in  the  decay  of  foodstuffs. 
The  disease  germs  that  we  take  into  the  body  when  we  are 
"exposed"  to  a  disease  are  not  numerous  enough  to  pro- 
duce much  toxin,  so  there  is  usually  a  period  of  time, 
called  the  incubation  period  (incubation  also  means 
"hatching"),  during  which  the  germs  are  multiplying, 
and  are  producing  enough  of  the  toxins  to  give  us  the 
symptoms  of  the  disease. 

423.  How  Germs  May  Be  Destroyed. — While  the 
disease  germs  that  get  into  the  body  do  not  always  cause 
disease,  because  of  the  power  of  the  white  corpuscles  and 
the  germicides  to  destroy  them,  we  are  not  safe  if  we 
depend  on  this  power  alone.  We  must  do  all  we  can  to 
destroy  the  germs  before  they  enter  the  body.  Hence 
we  cleanse  the  body  and  its  clothing,  and  our  dishes  and 
floors.  Since  food  for  man  is  often  food  for  germs,  we 
cook  or  bake  most  of  our  food.  The  high  temperature  of 
boiling  water  and  of  the  oven  destroys  the  germs. 

To  some  of  us  the  wiping  up  of  dust  ("dusting  the 
house")  may  seem  an  unnecessary  performance.  But  if 
a  house  is  to  be  safe,  the  dust  that  collects  must  be  re- 
moved carefully;  it  may  contain  deadly  germs.  If  a 
house  contains  a  great  deal  of  heavy  furniture  and  much 
bric-a-brac,  the  labor  of  house  cleaning  is  so  great  that 
it  may  not  be  carried  out  often  enough.  The  average 
family  needs  to  reduce  greatly  the  quantity  of  its  house 


HOW  HOUSEFLY  AND  MOSQUITO  AFFECT  HEALTH     429 

furnishings,  if  it  is  to  make  any  real  headway  against  dust 
and  the  disease  germs  which  the  dust  contains. 

Light  and  air  are  nature's  agents  for  the  destruction  of 
germs  "in  the  open";  we  need  these  in  our  houses  also 
(cf.  §  246).  One  of  the  worst  results  of  dust  and  dirt  in 
the  house  is  that  they  cover  up  the  germs,  and  prevent 
light  and  air  from  getting  at  them.  As  we  call  the  in- 
vasion of  our  bodies,  our  homes,  or  our  clothing,  by  harm- 
ful germs,  infection,  so  we  call  the 
destruction  of  such  germs  disinfection. 
The  agents,  or  materials,  that  cause 
germ  destruction  we  call  disinfectants. 
The  most  common  disinfectants  of  the 
household  are  soap  and  hot  water. 
There  are  also  chemical  disinfectants 
that  are  very  useful  for  special  pur- 
poses (cf.  §  438).  Disinfection  by  gases 
is  called  fumigation. 

424.  How  the  Housefly  and  Mosquito 
Affect  Public  Health.— There  is  little  or 
no  use  in  arguing  the  question  whether 
or  not  the  fly  does  anything  for  man; 
we  have  abundant  evidence  of  what  he  Fig.  sos. 

does  to  man.  Flies  grow,  as  maggots,  in  Foot  ofiangSnflyiWith 
the  body  waste  of  animals;  they  feed  in 
all  manner  of  dirty  places;  they  enter  sickrooms,  and  come 
away  loaded  with  disease  germs  (Fig.  303).  Not  only  do 
germs  cling  to  the  fly,  but  they  are  present  in  the  dis- 
charges of  its  body  (' i  fly  specks  ") .  This  evidence  against 
the  fly  is  enough  to  exclude  it  from  our  tables,  our  dishes, 


430  SANITATION 

and  our  faces.  We  should  make  every  effort,  by  the  use 
of  good  screens,  to  keep  flies  out  of  our  houses,  and  away 
from  our  food.  Especially  should  we  protect  little  chil- 
dren from  them. 

But  while  the  slogan  "Swat  the  fly!"  rings  through  the 
land,  we  must  remember  that  the  adult  fly  is  largely  what 
we  make  it.  It  does  not  travel  far.  The  germs  that  it 
carries  it  gets  from  the  neighborhood  where  it  lives,  and 
where  we  live.  To  make  a  campaign  against  the  fly 
effective,  we  need  to  keep  our  neighborhood  clean  and 
sanitary.  Flies  will  not  breed  if  there  are  no  dirty  places, 
such  as  manure  heaps  and  heaps  of  kitchen  waste,  in  which 
the  adult  fly  can  lay  its  eggs.  Flies  will  not  carry  germs 
from  house  to  house  if  every  house  is  properly  screened, 
and  if  we  take  care  to  destroy  the  disease  germs  that 
come  from  sickness.  Flies  will  not  find  food,  out  of  doors, 
if  crumbs  and  dish  water  are  not  thrown  into  the  yard, 
and  if  garbage  is  carefully  covered,  removed,  and  de- 
stroyed. So,  to  get  rid  of  the  fly  and  the  long  train  of 
troubles  for  which  it  is  responsible  we  need  not  only  to  kill 
it  when  we  find  it,  but  we  must  keep  our  neighborhood  clean. 
If  we  do  this,  the  fly  cannot  develop  and  multiply  there. 

What  is  true  of  the  fly  is  largely  true  of  the  mosquito. 
Its  breeding  habits  are  well  known  (cf.  §  339,  Fig.  264); 
the  eggs  must  be  laid  in  water.  In  inserting  its  sharp 
proboscis  into  the  skin  of  a  sick  person,  it  becomes  in- 
fected, and  then  introduces  the  infection  into  the  body  of  a 
person  who  is  well.  The  region  about  Rome  has  long 
been  filled  with  deadly  malaria,  but  we  now  know  that 
people  may  live  there  without  fear,  if  they  are  screened 
against  malaria  mosquitoes. 


DANGER  IN  FOOD  431 

Like  the  fly,  the  malaria  mosquito  is  a  "home  product."  It  lives 
very  near  the  place  where  it  was  hatched.  To  get  rid  of  it,  we  must 
destroy  its  breeding  places.  Open  cisterns,  wells,  rain  barrels,  water- 
ing troughs,  ditches,  puddles,  sagging  eaves  troughs,  broken  crockery, 
and  tin  cans,  anything  that  can  hold  water,  all  these  give  the  mosquito 
its  opportunity.  All  unnecessary  holders  of  water  should  be  removed 
or  buried;  the  others  should  be  carefully  screened.  Ditches  should  be 
drained.  Puddles,  cisterns,  and  barrels  that  contain  "wigglers" 
should  be  treated  with  a  little  kerosene  (cf.  §  339),  and  then  screened. 
Cities  often  suffer  needlessly  from  mosquitoes,  because  the  creatures 
are  allowed  to  develop  in  street  catch  basins.  The  catch  basin  receives 
the  water  that  comes  from  the  street,  and  the  water  that  remains  in  it 
acts  as  a  "water  seal"  to  the  street  sewer,  just  as  the  "trap"  does  to 
the  house  sewer  (cf.  §  236) .  If  there  is  no  rain  for  some  time,  and  if  the 
catch  basin  is  not  "flushed  out,"  the  standing  water  permits  the  mos- 
quito to  breed.  A  little  kerosene  thrown  into  the  catch  basins  would 
rid  the  neighborhood  of  the  nuisance. 

425.  Danger  in  Food. — If  the  body  were  unprotected, 
a  single  germ  might  cause  a  disease.  But  this  is  rarely 
possible.  A  few  germs  are  usually  destroyed  at  once  by 
the  blood.  But  a  large  number  (many  millions)  may  be 
introduced  into  the  body  in  a  single  bite  of  bad  food,  or 
in  a  mouthful  of  infected  water.  So  we  need  to  be  very 
careful  about  the  food  we  eat.  Only  persons  with  clean 
hands  and  clean  clothing  should  prepare  and  handle 
food,  and  food  should  be  stored  only  in  clean,  protected 
places  (Fig.  304).  If  customers  were  clean  themselves, 
and  were  particular  about  the  cleanliness  of  what  they 
buy  and  use,  their  groceries,  meat  markets,  bakeries, 
fruit  stores,  candy  kitchens,  laundries,  milk  depots,  etc., 
would  be  clean  too. 

We  must  be  particular,  also,  about  tainted,  or  decayed,  food.  Over- 
ripe fruit  is  always  to  be  suspected.  Many  a  household  is  so  anxious 


432 


SANITATION 


not  to  waste  food  that  it  eats  suspected  food  "to  save  it."  This  is  the 
worst  kind  of ' '  saving, ' '  for  the  food  usually  makes  some  one  of  the  family 
ill,  and  causes  a  waste  a  hundred  times  as  great  as  any  possible  saving. 


Fig.  304. 
Exposed  food,  which  is  not  protected  from  flies  and  street  filth,  is  covered  with  germs. 


Milk  is  especially  liable  to  infection.     Ever  so  many 
epidemics  of  children's  diseases,  such  as  scarlet  fever  and 


DANGER  IN  FOOD 


433 


diphtheria,  have  been  traced  to  an  infected  milk  supply. 
Milkmen  having  the  diseases  in  their  own  families  have 
again  and  again  been  found  delivering  milk  to  other  fam- 
ilies. Typhoid  fever  and  consumption  are  likewise  spread 


Only 
Bottled 


Buy  Only  From  Clean  Alii  km  en 
Aiever  Bug  In  Store  5vtarming  With  Flies 

AlERE'6  A  CflEAP/iO/IE-AlADE  ICE- 


FOR  KEEPING  BABY'S 

Co*t:  —  Less  tha^n  twenty  -five,  cent* 


A- Wooden  box.  B-Tin  collar,  C-Tin  pail  with  cover  (pai I  talUr  than 
milk  bottle;.  D-  Sawdust  packed  around  out».de  o/  tin  collar;  E.-  Paper  feck- 
<d  en  inside  <?  box  cover,  F-  Ice  packed  around  bottle  o/  milk  in  pail. 

Fig.  305. 
There  is  need  of  ice  to  keep  milk.     Educational  Poster,  Chicago  Health  Department. 

by  infected  milk.  If  we  buy  milk  from  a  small  dairy,  we 
should  visit  the  dairy,  or  ask  some  competent  person  to 
do  so,  to  see  if  the  conditions  are  sanitary,  and  if  the  cows 
are  healthy  and  well  fed.  If  we  buy  in  a  large  city,  and 


434 


SANITATION 


cannot  inspect  the  supply  directly,  we  should  ask  the 
health  authorities  to  make  frequent  examinations  of  the 
milk,  so  that  we  may  be  reasonably  sure  that  it  is  safe. 

Milk  "spoils "  most  rapidly,  of  course,  in  warm  weather, 
just  when  babies  suffer  most  from  the  heat.  If  to  their 
weakened  bodies  we  add  germ-laden  milk,  the  results  are 
sure  to  be  serious.  The  number  of  deaths  of  young 
children,  in  summer,  is  very  great,  and  many  of  them  can 
be  prevented.  Germs  cannot  develop  so  rapidly  in  cold 

milk  as  in  warm  milk, 
hence  there  should  be  a 
refrigerator,  of  some  sort, 
in  every  family  where 
there  are  children  (Fig. 
305).  Many  cities  fur- 
nish free  ice,  or  inexpen- 
sive ice,  to  the  very  poor, 
as  this ' '  saves  the  babies . ' ' 


Fig.  303. 

The  Wrong  and  the  Right  Kind  of  Nursing 
Bottles. 


In  most  cases  children  can 
digest  pasteurized  milk  (so 
called  from  the  celebrated 
French  scientist,  Pasteur) . 

The  process  of  pasteurizing  is  simple  and  inexpensive,  the  apparatus 
consisting  only  of  a  covered  pail,  with  a  hole  in  the  cover  for  a 
thermometer.  The  bottle  containing  milk  is  placed  in  the  pail, 
the  pail  is  filled  with  water  almost  to  the  mouth  of  the  bottle, 
the  cover  and  thermometer  are  put  in  place,  and  the  pail  is  heated. 
A  temperature  of  68.3°  C.  (155°  F.)  maintained  for  half  an  hour, 
or  of  77°C.  (170°  F.)  for  5  minutes,  kills  the  disease  germs  of  the 
milk.  The  milk  is  then  cooled  rapidly,  and  stored  in  a  refriger- 
ator. The  bottles  used  for  the  feeding  of  babies  often  spoil  other- 
wise good  milk  (Fig.  306).  Those  with  a  long,  slender  rubber  tube 


DANGER  IN  FOOD 


435 


are  especially  dangerous,  for  germs  collect  in  the  tube,  and  are  not 
easily  removed.  It  is  on  such  details  as  this  that  the  life  of  many  a 
baby  depends. 

Preservatives. — Because  chemicals  destroy  disease 
germs,  many  dealers  in  foods,  and,  unfortunately,  some 
housekeepers,  argue  that  chemicals  may  properly  be  used 
to  destroy  the 
germs  in  food, 
and  to  prevent 
natural  decay. 
Why  not  use  sul- 
phur dioxide  to 
preserve  dried 
apples,  formalde- 
hyde to  preserve 
milk  and  canned 
corn,  salicylic  acid 
to  preserve  fruit, 
and  borax  to  pre- 
serve meat?  The 
answer  is  that 
these  preserva- 
tives are,  sooner 
or  later,  poisons 
to  the  body.  The 
least  harmful 
thing  they  do  is 
to  prevent  food 

from  digesting  properly.  We  eat  the  food,  but  the  body 
does  not  get  from  it  the  necessary  nutrients.  Such  food 
is  really  wasted. 


Fig.  307. 

There  is  death  in  the  public  drinking  cup.     Educational 
Poster,  Chicago  Health  Department. 


436 


SANITATION 


Preservatives  in  milk  are  very  injurious  to  children. 
The  small  amount  of  chemicals  may  do  only  a  slight  dam- 
age to  a  grown  person,  for  milk  is  only  a  small  part  of  his 
food;  but  for  the  little  child  milk  is  almost  the  whole  diet. 
Milk  that  does  not  sour  in  24  hours,  or  less,  at  a  summer 
temperature,  needs  to  be  tested  for  preservatives. 


Fig.  308. 
Sanitary  Drinking  Fountain. 

426.  Contaminated  Cups,  Money,  Etc. —  Public  drink- 
ing cups  are  another  source  of  great  danger  (Fig.  307); 
many  diseases  can  be  spread  by  their  use.  The  practice 
of  drinking  from  one  "family"  dipper  is  bad  enough,  but 
how  much  worse  it  is  for  all  the  people,  whether  diseased 
or  well,  to  drink  from  the  same  cup  when  they  are  in 
public  buildings,  or  on  the  train,  or  at  public  fountains. 


TYPHOID  AND  SEWAGE  437 

We  ought  to  have  our  own  drinking  cups  when  we  travel, 
so  that  we  shall  not  give  a  disease  to  any  one  else,  nor  run 
the  risk  of  catching  one  from  others.  We  ought  to  have 
our  own  cups  at  school,  too,  unless  the  school  has  a  sani- 
tary fountain  (Fig.  308).  To  put  into  the  mouth  objects 
that  have  been  handled  by  others  is  just  as  bad  as  to  use 
dirty  drinking  cups. 

Public  towels  and  soap,  as  these  are  found  in  public  washrooms 
and  in  many  hotels,  are  full  of  danger.  . 

All  money,  especially  paper  money,  that  has  been  carried  about  in 
unclean  pockets,  and  handled  with  dirty  fingers,  is  "tainted."  The- 
examination  of  paper  money  by  bacteriologists  shows  that  the  money 
has,  sticking  to  it,  germs  of  almost  every  variety,  including  those  of  our 
worst  diseases.  Hands  should  be  washed  after  they  have  handled 
money,  and  before  they  are  used  about  food  or  the  face.  Certainly  no 
cashier  ought  to  be  expected  to  eat  his  dinner,  and  to  "make  change," 
between  bites,  for  customers. 

427.  Typhoid  and  Sewage. — Typhoid  fever  is  one  of 
man's  most  serious  diseases.  There  are  perhaps  250,000 
cases  of  it  in  a  year  in  the  United  States  alone,  with  up- 
wards of  25,000  deaths.  The  bacteria  that  cause  it 
(cf.  §  324)  are  taken  into  the  body  through  the  mouth,  in 
food  or  water.  In  the  small  intestine  they  multiply 
rapidly,  and  produce  toxins  that  pass  into  other  parts  of 
the  body.  The  body  waste  from  the  intestines  and  kid- 
neys of  a  typhoid  patient  contains  large  amounts  of  the 
germs.  If  the  germs  are  not  destroyed,  they  get  into  the 
soil  and  into  sewage.  From  the  soil  they  may  get  into 
garden  vegetables,  and  may  be  carried,  by  seepage  water, 
into  wells.  The  germs  may  get  into  milk  from  the  water 
with  which  milk  cans  are  rinsed,  or  from  some  one  who 


438  SANITATION 

has  the  disease,  or  from  some  one  who  handles  the  milk 
with  dirty  hands.  If  the  sewage  is  emptied  into  the 
stream  or  lake  from  which  a  community  gets  its  water, 
the  whole  community  is  in  danger  of  having  the  disease. 
Typhoid  germs  have  been  found  in  oysters  that  grew  near 
the  outlets  of  sewers.  In  some,  or  all,  of  these  ways  the 
typhoid  germs  of  one  who  has  the  disease  may  find  their 
way  into  the  alimentary  canals  of  new  victims. 

An  epidemic  (the  word  means  "among  the  people")  that  occurred 
in  1885  in  Plymouth,  Pennsylvania,  is  often  used  to  show  the  connec- 
tion between  drinking  water  and  typhoid.  Plymouth  had  8,000 
inhabitants,  and  obtained  its  water  chiefly  from  a  clear,  pure  mountain 
stream.  In  the  early  spring,  while  there  was  still  snow  on  the  ground, 
one  man  living  near  the  stream,  but  far  from  the  town,  had  typhoid 
fever.  His  body  waste  was  thrown  on  the  ground,  near  the  stream. 
When  the  snow  melted,  the  typhoid  germs  were  carried  into  the  stream, 
and  soon  produced  a  dreadful  epidemic  in  Plymouth.  Within  a  few 
weeks  there  were  1,104  cases  of  typhoid  and  114  deaths.  The  cost  of 
this  epidemic  to  that  community  was  estimated  as  not  less  than  half  a 
million  dollars  (Sedgwick). 

Persons  have  been  found  who  continue  to  harbor  the  germ  long  after 
they  recover  from  the  disease,  and  who  communicate  the  disease  to 
multitudes  of  others.  Recently,  a  medical  journal  described  an 
epidemic  in  a  western  city,  in  which  85  persons  had  typhoid  because 
they  ate  " macaroni  and  cheese"  that  had  been  prepared  by  a  " typhoid 
carrier."  The  person  in  question  was  a  woman  65  years  old,  who  had 
never  consciously  had  typhoid  fever  and  who  was  apparently  in  good 
health. 

428.  Exercises. 

1.  Which  house  will  have  the  better  chance  of  fighting  disease 
germs  successfully,  the  one  with  all-over,  tacked  carpets,  or  the  one 
with  loose  rugs?  Why?  The  one  in  which  a  feather  duster  is  used, 
or  the  one  in  which  the  housekeeper  removes  dust  with  a  damp  cloth? 
The  one  in  which  children  are  taught  to  wipe  their  feet  outside  of  the 


EXERCISES  439 

house,  or  the  one  in  which  street  and  barnyard  filth  is  brought  into  the 
house? 

2.  Why  is  it  better  to  have  little  bric-a-brac  on  mantels  arid  walls, 
rather  than  much?     To  have  "open"  plumbing,  rather  than  plumb- 
ing enclosed  in  wooden  cupboards?    To  have  a  light,  airy  cellar, 
rather  than  a  dark,  damp  one?    To  do  sweeping  with  a  carpet  sweeper, 
rather  than  with  a  broom?    What  are  the  advantages  of  "vacuum 
cleaning"  apparatus? 

3.  Why  should  you  not  wipe  your  eyes  with  your  fingers?    Allow 
your  teeth  to  remain  uncleaned?    Cough  with  your  face  to  the  table? 
Carry  drinking  glasses  with  your  fingers  inside  the  glasses?    Turn 
the  leaves  of  a  book  with  fingers  moistened  by  saliva?    Put  pencils  into 
your  mouth? 

4.  Which  would  you  expect  to  be  more  contaminated  with  germs, 
one-dollar  bills  or  ten-dollar  bills?    Why? 

5.  Can  a  cistern  be  kept  clean  if  birds  are  allowed  to  live  on  the 
roof  or  in  eaves  troughs? 

6.  Name  all  the  ways  in  which  a  community  can  guard  itself  against 
typhoid  fever. 

7.  Find  out  from  a  physician  or  a  well-digger  how  a  well  should  be 
constructed  and  protected,  so  that  surface  water  may  not  get  into  it 
(cf.  §  81.) 

8.  How  can  the  germs  in  drinking  water  be  removed  or  destroyed? 
(Cf.  §  83).     Is  ice  ever  dangerous  to  public  health? 

9.  What  do  you  think  of  the  following  as  sanitary  practices :  Locat- 
ing of  bakeries  in  cellars?    In  tenement  houses?    Having  milk  depots 
in  cellars?     Delivering  milk  in  cans?    Delivery  of  milk  in  bottles,  but 
in  open  wagons?    Handling  of  milk  bottles  by  the  mouths  of  the 
bottles? 

10.  Do  you  think  it  safe  to  put  away  furs,  winter  caps,  underwear, 
and  clothing  in  a  closet  or  trunk,  without  disinfecting  them,  and  then 
to  wear  them  again  in  the  fah1? 

11.  What  objection  is  there  to  having  much  furniture,  and  draperies, 
bookcases,  etc.,  in  a  sickroom? 

12.  What  does  sediment  at  the  bottom  of  a  milk  bottle  indicate? 
Why  ought  the  mouth  of  a  milk  bottle  to  be  wiped  before  the  bottle  is 
opened? 


440  SANITATION 

13.  Why  should  dish  cloths  and  dish  towels  be  sterilized  often? 

14.  Find  out  when  bread  is  delivered  to  a  grocery  in  your  neighbor- 
hood, and  watch  the  process.     Write  a  description  of  the  process,  and 
criticize  it  from  the  sanitary  point  of  view. 

15.  In  the  same  way  study  and  criticize  the  handling  of  milk  in  your 
own  house  and  in  that  of  some  neighbor. 

16.  How  is  garbage  disposed  of  in  your  neighborhood?    Watch  the 
process  of  garbage  collection,  and  criticize  it.    How  could  the  house- 
holder help  in  making  the  process  more  sanitary?     How  could  the 
collector  help? 


429.  Tuberculosis,  or  Consumption. — Consumption  is 
due  to  a  germ  (the  tubercle  bacillus),  and  is  " caught"  by 
one  person  from  another.  Most  persons,  perhaps  90  out 
of  every  100,  are  attacked,  at  some  time  or  other,  by  the 
germ.  Usually  the  body  is  able  to  overcome  the  disease, 
and  we  do  not  know  that  we  have  been  attacked.  But 
if  the  body  once  yields  to  the  disease,  we  become  weaker 
and  weaker,  and  less  able  to  shake  it  off.  It  is  one  of  the 
triumphs  of  modern  medicine  that  we  know  we  can  over- 
come consumption  if  we  treat  it  in  its  early  stages.  We  do 
not,  therefore,  need  to  give  up  if  we  have  the  disease,  but 
can  use  simple,  easy  means  to  be  cured.  The  chief  things 
we  must  do  are  to  live  in  the  open  air,  to  be  warmly  clothed, 
and  to  eat  an  abundance  of  simple,  nourishing  food  (cf. 
§  246;  also  Fig.  309).  If  one  has  a  suspicion  that  he  has 
tuberculosis,  he  ought  not  to  hide  the  fact,  nor  to  try 
patent  medicine  " cures,"  but  to  see  a  physician  at  once. 
When  a  large  area  of  the  lungs  has  become  diseased,  it  is, 
of  course,  harder  for  us  to  be  cured;  it  may  be  impossible. 
The  tuberculosis  germ  is  usually  expelled  from  the  body 
in  the  sputum,  or  "spit,"  which  the  consumptive  coughs 


TUBERCULOSIS  OR  CONSUMPTION 


441 


up  from  his  lungs.     This  should  never  be  scattered,  but 
should  be  entirely  destroyed.     The  best  way  is  to  burn  it. 

By  the  modern  method,  consumption  can  be  cured  in  any  climate, 
but  a  cold,  dry  climate  is  the  best.  To  be  cured,  one  does  not,  there- 
fore, need  to  go  away  from  a  cold  climate,  as  men  formerly  thought, 
Neither  is  tuberculosis  inherited,  as  men  used  to  believe.  The  disease 
can  come  only  from  the  entrance  of  the  bacilli  into  the  lungs.  But 
people  can  inherit  a  weak  resisting  power,  so  that  they  need  to  use  more 


Fig.  309. 
Open  Air  Cottage  of  a  Tuberculosis  Sanitarium. 

care  to  avoid  taking  the  disease  than  do  the  children  of  non-consump- 
tive parents.  One  reason  why  members  of  the  same  family  often  get 
the  disease  is  that  the  germs  are  not  destroyed  with  sufficient  care,  but 
are  allowed  to  spread  through  the  house.  They  thus  go  from  the  sick 
member  of  the  family  to  those  that  are  well.  Sputum  should  not  be 
allowed  to  dry,  and  the  dishes,  linen,  and  clothing  of  the  patient  should 
be  thoroughly  disinfected. 

Tuberculosis  germs  remain  in  houses,  and  one  family  after  another, 
by  living  in  an  infected  house,  may  furnish  victims  for  the  disease. 
When  we  plan  to  move  into  a  house,  we  ought  to  be  interested,  not  only 
in  the  view  and  the  wall  paper,  but  also  in  the  sanitary  history  of  the 
house,  so  that  we  may  know  what  risk  we  are  taking  by  living  in  it. 


442  SANITATION 

430.  Spitting     in     Public. — Public-health    authorities 
everywhere  are  trying  to  stop  the  practice  of  expectorat- 
ing, or  ' '  spitting,"  in  public  places.     The  habit  is  not  only 
disgusting  and  indecent,  but  dangerous.     This  is  clear 
from   what    we   have   learned    of   tuberculosis.     If   we 
remember  that  a  multitude  of  germs  is  expelled  from  the 
body  in  the  act  of  "  spitting, "  and  that  the  germs  cast 
forth  become  a  part  of  the  dust  that  all  passers-by  must 
breathe,  we  can  see  what  a  dangerous  indulgence  public 
spitting  is. 

431.  Colds. — We  often  speak  lightly  of  colds;  if  suf- 
fering from  one,  we  say  we  have  "only  a  cold."     But 
colds  need  to  be  included  in  our  list  of  serious  diseases,  if 
for  no  other  reason  than  that  they  are  so  common,  and 
that  they  lower  the  working  ability  of  so  many  people. 
Colds  are  also  serious  because  they  are  often  the  begin- 
nings of  consumption,  pneumonia,  diphtheria,  etc.     The 
cold  does  not  cause  these  diseases  directly,  but  it  lowers 
the  power  of  the  body  to  resist  dangerous  germs. 

Colds  are  communicated  from  one  person  to  another;  the  one  who 
has  a  cold  ought  to  exercise  care,  so  that  he  may  not  pass  it  on  to  others. 
A  cold  that  " hangs  on"  needs  a  physician's  care,  especially  if  it  causes 
difficult  breathing  and  fever.  If  it  is  "only  a  cold,"  the  avoiding  of 
drafts,  care  in  clothing,  and  the  eating  of  light  food,  especially  of  liquid 
food,  are  usually  all  that  is  needed  to  cure  it.  The  old  saying  is  that 
if  you  " stuff  a  cold"  (that  is,  overeat),  you  will  need  to  "starve  out  a 
fever. "  But  if  a  cold  makes  us  weak  and  chilly,  a  day  or  two  spent  in 
bed  will  be  of  the  greatest  possible  help.  Time  will  actually  be  saved, 
if  we  do  not  work  when  we  are  unfit  for  work. 

We  often  "catch  cold"  after  we  have  been  overheated  by  the 
wearing  of  too  heavy  clothing,  or  by  living,  even  for  a  little  while,  in 


ANTITOXINS  443 

rooms  that  are  hot  and  poorly  ventilated  (cf.  §  247).  A  bad  habit, 
which  too  many  of  us  have,  is  that  of  going  into  warm  buildings,  in 
cold  weather,  without  removing  our  outer  wraps;  when  we  go  out 
again,  overheated,  we  are  in  danger  of  serious  trouble. 

432.  Diphtheria. —  Diphtheria  is  often  mistaken  for  a 
cold;  this  fact  is  one  reason  why  a  cold  should  not  be  left 
to  chance,  but  should  be  treated  by  a  physician.     If  a 
child  has  a  croupy  cough  that  comes  not  only  at  night, 
but  also  during  the  day,  its  throat  should  be  examined  at 
once.     Small,    tough,    grayish-white    "patches"    in   the 
throat  indicate  diphtheria.     Membranous  croup  is  diph- 
theria in  the  larynx. 

The  germ  of  diphtheria  is  scattered  abroad  by  the 
violent  coughing  of  the  patient  and  by  the  discharges  from 
his  nose  and  throat.  All  cloths  containing  the  discharges 
should  be  disinfected  or  burned.  After  one  has  had  the 
disease,  he  may  have  the  germs  in  his  throat  for  months, 
and  may  give  the  disease  to  those  with  whom  he  comes  in 
contact.  The  germs  may  also  get  into  the  throat  of  a 
healthy  person,  and  yet  be  held  in  check  because  of  the 
person's  " resisting  power."  This  healthy  person  may, 
however,  infect  milk,  handkerchiefs,  drinking  cups,  dishes, 
etc.,  and  pass  the  germs  on  to  others  who  cannot  resist 
the  disease.  The  cause  of  the  severe  illness  in  diphtheria 
is  usually  its  poisonous  toxin,  although  sometimes  the 
throat  is  closed  by  the  diphtheria  membrane.  Death 
sometimes  comes  in  two  or  three  days. 

433.  Antitoxins. — The  word  antitoxin  means  "against 
toxin."     When  germs  get  into  the  body,  they  produce 
toxins  (cf.  §  422).     To  protect  itself,  the  body  produces 


444  SANITATION 

not  only  white  corpuscles  and  germicides,  which  kill  the 
germs  themselves,  but  also  substances  that  neutralize 
the  effect  of  the  toxins.  These  are  the  antitoxins.  For 
every  toxin  that  germs  produce,  the  body  probably  forms 
an  antitoxin.  In  diphtheria  the  patient  may  not  be  able 
to  produce  enough  antitoxin  to  stop  the  disease,  but  if  he 
is  helped  by  the  addition  of  some  diphtheria  antitoxin  to 
his  blood,  he  may  win  his  fight  against  the  germs.  Like- 
wise, if  one  who  has  been  exposed  to  the  disease  is  treated 
with  antitoxin,  the  germs  may  not  be  able  to  develop 
enough  of  the  toxin  to  cause  the  disease. 

The  diphtheria  antitoxin  is  produced  in  the  body  of  the  horse.  The 
method  is  as  follows: 

Germs  taken  from  some  one  who  has  the  disease  are  allowed  to 
multiply  in  a  rich  nutrient  like  beef  broth.  They  thus  produce  a  great 
deal  of  the  toxin.  The  germs  are  then  filtered  out,  and  the  liquid 
containing  the  toxin  is  injected  under  the  skin  of  a  horse.  The  horse's 
blood  produces  antitoxin  to  neutralize  the  toxin.  As  more  and  more 
toxin  is  injected,  more  and  more  antitoxin  is  produced.  The  horse 
becomes  immune  to,  or  "fortified  against/'  the  Joxin.  Then  blood  is 
drawn  from  the  horse,  and  is  clotted  and  filtered.  The  resulting 
filtered  liquid  is  the  antitoxin  serum.  When  some  of  this  is  introduced, 
under  the  skin,  into  the  human  body,  it  makes  the  body  immune,  or 
at  any  rate  helps  in  making  it  immune,  to  the  toxin  produced  by  the 
diphtheria  germ. 

The  records  of  many  hospitals  show  that  while  before  the  days  of 
antitoxin  there  used  to  be  30  to  50  deaths  out  of  every  100  cases  of 
diphtheria,  the  deaths  since  the  introduction  of  antitoxin  are  only 
from  11  to  18  in  100  cases.  If  the  antitoxin  is  pure,  and  if  it  is  used  as 
soon  as  the  disease  shows  itself ,  there  are  practically  no  deaths. 

434.  SmaUpox.— Typhoid,  tuberculosis,  and  diph- 
theria are  germ  diseases,  but  they  are  not  accompanied  by 


VACCINATION  445 

a  "breaking  out"  (eruption)  of  the  skin.  Smallpox 
belongs  to  the  eruptive  diseases ;  the  sores,  when  they  heal, 
leave  the  "pock"  marks  that  give  the  disease  its  name. 
Up  to  the  year  1800  almost  everybody  expected  to  have 
smallpox;  few  seemed  to  have  sufficient  resisting  power  to 
ward  off  the  disease.  The  loss  of  life  in  smallpox  epi- 
demics was  enormous:  between  the  years  1700  and  1800 
probably  600,000  persons,  on  the  average,  died  of  the 
disease  every  year.  But  the  practicing  of  vaccination 
and  the  progress  made  in  sanitary  science  have  combined 
to  reduce  the  deaths  from  the  disease  to  comparatively 
small  numbers. 

Vaccination  for  smallpox  was  preceded  by  inoculation,  which  may 
be  defined  as  artificial  infection.  Inoculation  consisted  in  putting 
some  of  the  " matter"  from  the  eruptions  of  a  smallpox  patient  under 
the  skin  of  a  person  who  was  well.  The  person  inoculated  chose  to 
have  the  disease  when  he  was  prepared  for  it,  rather  than  when  he  was 
not  prepared.  He  usually  had  the  disease  in  a  mild  form,  and  then 
was  immune  for  life.  The  method  of  inoculating  well  persons  came 
from  China  to  Constantinople  (we  do  not  know  when);  from  Con- 
stantinople it  spread,  in  about  1720,  to  Western  Europe  and  to  Amer- 
ica. One  disadvantage  of  this  early  method  of  inoculation  was  that 
the  persons  treated  could  give  the  disease  to  others,  hence  they  had  to 
be  isolated,  or  kept  apart.  There  were  also  some  serious  accidents 
in  inoculation,  because  men  did  not  know  of  the  existence  of  germs,  and 
therefore  did  not  know  the  meaning  of  sanitary  cleanliness.  If  the 
" matter"  introduced  into  the  body  of  the  well  person  was  infected 
with  other  germs,  or  if  the  instruments  used  were  not  clean,  the  person 
inoculated  "caught"  other  serious  diseases. 

435.  Vaccination. — The  discovery  of  vaccination  (vacca 
means  "a  cow")  by  Jenner  came  in  1796.  Jenner  took 
the  "matter"  formed  in  cowpox  (smallpox  of  the  cow), 


446 


SANITATION 


and  introduced  this  "vaccine  virus"  under  the  skin  of  a 
man.  He  thus  found  that  he  could  produce  in  the  man  an 
immunity  to  the  disease.  Vaccination  (Fig.  310)  usually 


AFTER 


Criminal  negligence  defaced 
thb  child  for  life. 

A  little  SC^r*  on  the  a^rrrz.  will  prevent 
thousands  of  sc^rs  on  the  fe>,ce. 

Fig.  310. 
Effect  of  Smallpox      Educational  Poster,  Chicago  Health  Department. 

produces  a  mild  inflammation  at  the  place  where  the 
virus  is  introduced;  this  is  due  to  the  growth  of  the  germs. 
The  germs  from  the  cow  are  so  much  weaker  than  those 
that  come  from  a  human  smallpox  patient  that  they  can- 
not produce  the  dreaded  disease,  but  their  presence  in 


OTHER  GERM  DISEASES  447 

the  blood  stimulates  the  body  to  produce  the  germicide 
for  the  smallpox  germ. 

The  germicide  seems  to  remain  in  the  blood  for  some  time,  perhaps 
for  years  in  some  persons,  and  protects  the  body  if  other  smallpox 
germs  enter.  In  some  persons,  however,  the  germicide  disappears  in 
less  than  a  year.  We  should  be  vaccinated  every  few  years,  or  more 
frequently  if  there  is  smallpox  near  us,  in  order  that  the  germicide 
may  always  be  present  in  the  body.  If  we  are  vaccinated  by  a  good 
doctor,  with  fresh  vaccine  virus,  there  is  no  danger.  The  doctor 
should  use  only  virus  that  has  been  purified,  so  that  it  cannot  contain 
other  infecting  germs.  We  should  be  vaccinated,  not  only  for  our  own 
sakes,  but  for  the  sake  of  others.  The  germs  of  smallpox  live  for 
months  in  a  dry  condition;  they  may  be  preserved  in  books,  clothing, 
letters,  etc.  Hence  we  can  never  tell  when  we  may  catch  the  disease, 
and  give  it  to  our  friends  and  neighbors.  We  are  not  wiser  than  the 
experience  of  the  last  100  years.  This  experience  teaches  us  that 
while  sanitary  living  helps  to  keep  the  germs  down,  it  cannot  help  us 
if  they  get  into  the  blood,  and  if  the  blood  has  not  prepared  the  proper 
germicide  for  our  defense. 

Vaccination  against  typhoid  fever  is  now  being  carried  out  with 
success,  especially  to  protect  armies  in  the  hard,  insanitary  conditions 
under  which  they  are  often  forced  to  live.  The  germs  of  typhoid  are 
cultivated  until  they  have  multiplied,  and  produced  their  toxins. 
Then  the  germs  are  killed,  and  small  amounts  of  the  dead  germs  and 
the  toxins  are  injected  under  the  skin  of  the  person  to  be  protected. 
Vaccination  against  typhoid  ought  to  be  an  additional  precaution,  not 
a  substitute  for  sanitary  measures. 

436.  Other  Germ  Diseases. — Scarlet  fever  and  measles 
are  eruptive  diseases,  just  as  smallpox  is.  Both  are 
highly  infectious,  and  both  come  chiefly  in  childhood. 
The  scarlet-fever  patient  often  suffers  little  from  the  first 
stages  of  the  disease,  but  has  very  serious  after-effects. 
These  may  produce  lifelong  injury,  even  if  they  do  not 


448  SANITATION 

cause  death.  The  discharges  from  the  nose  and  mouth 
are  very  infectious;  so  is  the  dead  skin  ("scales"),  which 
the  patient  "sheds"  for  some  time  after  recovery.  No 
one  recovering  from  the  disease  should  be  allowed  at 
large  until  the  last  traces  of  scaling  have  disappeared,  or 
he  will  scatter  the  infection  broadcast.  Measles  is 
infectious  from  the  very  first.  It  "breaks  out"  not  only 
in  the  skin,  but  in  the  mucous  membrane  of  the  mouth, 
throat,  and  air  passages.  The  eruption  has  a  charac- 
teristic "measly"  odor.  The  after-effects  of  measles  are 
often  very  serious,  for  the  disease  leaves  the  throat  and 
lungs  weak,  so  that  there  is  danger  of  pneumonia  and 
consumption.  It  also  weakens  the  eyes.  Hence  the 
patient  should  not  be  allowed  in  a  bright  light,  and 
he  should  not  be  permitted  to  read  until  he  has  fully 
recovered. 

Pneumonia  (nu-mon'ya)  is  one  of  our  worst  diseases, 
especially  in  cities.  It  is  caused  chiefly  by  one  kind  of 
germ,  called  pneumococcus  (nu'-mo-kok-iis),  which  may 
grow  in  any  or  all  of  the  air  passages.  Pneumonia  attacks 
many  of  the  larger  animals  and  these  may  infect  man. 
The  germs  are  carried  from  one  patient  to  another  in  the 
sputum,  and  in  the  discharges  from  the  nose.  The  germs 
of  pneumonia  have  been  found  in  the  throat  of  most  per- 
sons, even  of  those  that  are  healthy,  but  they  are  held  in 
check  by  the  body's  resistance.  A  severe  cold,  some 
sudden  exposure,  or  a  weakening  of  the  body,  may  give 
them  their  opportunity  (cf.  §  407).  It  is  for  us  to  keep  the 
body  in  good  condition,  and  to  exercise  the  lungs  by 
breathing  deeply  of  fresh  air  (cf.  §  391),  so  that  the  germs 
may  not  get  a  secure  foothold.  The  danger  in  pneumonia 


OTHER  GERM  DISEASES  449 

is  partly  due  to  the  fact  that  the  lung  cells  may  be  covered 
up  by  the  growth  of  the  germs;  the  chief  danger,  however, 
is  from  the  toxin,  which  may  stop  the  action  of  the  heart. 

We  have  already  learned  that  malaria  is  carried  by  certain  mos- 
quitoes (cf.  §  424) ;  yellow  fever  is  carried  in  the  same  way.  But  while 
one  variety  of  mosquitoes  (anopheles)  carries  the  germ  of  malaria,  an 
entirely  different  variety  (stegomyia;  steg-o'-nrf-ya)  carries  the  yellow 
fever  germ.  Yellow  fever  has  long  been  the  pest  of  tropical  and  sub- 
tropical countries,  and  has  been  greatly  dreaded  in  our  own  southern 
states.  When  the  United  States  took  up  the  administration  of  Cuba, 
in  1898,  it  had  before  it  the  problem  of  a  general  "  cleaning  up,"  and  of 
getting  rid  of  the  yellow-fever  mosquito.  It  had  the  same  problem  to 
solve  before  it  could  dig  the  Panama  Canal.  If  houses,  especially 
those  in  which  there  is  yellow  fever,  are  carefully  screened  against 
mosquitoes,  and  if  the  breeding  places  of  the  mosquitoes  are  destroyed, 
the  disease  can  be  kept  under  control. 

Tetanus  (tet'-a-nus),  or  lockjaw,  is  a  disease  we  hear  most  about 
after  the  celebration  of  an  "insane"  Fourth  of  July,  when  there  have 
been  many  accidents  with  toy  pistols,  firecrackers,  toy  cannon,  and 
fireworks.  The  skin  is  so  good  a  protection  for  the  body  that  although 
tetanus  germs  are  often  on  the  skin  they  do  not  get  into  the  body. 
But  flying  particles  of  the  "caps,"  wads,  and  paper  of  explosives  carry 
the  germs  through  the  skin.  The  toxin  produced  by  the  germs  is  very 
powerful,  causing  a  contraction  and  stiffness  of  the  muscles,  first  of 
those  of  the  face,  and  afterwards  of  those  of  other  parts  of  the  body. 
Hence  the  name  "lockjaw."  Tetanus  germs  grow  in  the  ground,  and 
away  from  the  air,  hence  they  may  be  present  on  rusty  nails  and  un- 
clean garden  tools.  Wounds  made  by  articles  that  have  been  in  or  on 
the  ground  should  be  dressed  carefully,  by  a  physician  if  possible. 

Rabies  (ra'-be-ez),  or  hydrophobia,  seems  to  be  produced  by  pro- 
tozoa that  grow  in  the  nerve  tissue  of  the  brain  and  spinal  cord.  The 
disease  is  "given"  to  dogs  and  cats  in  the  bites  and  scratches  which 
they  receive  from  other  creatures  that  have  the  disease.  The  infected 
dogs  and  cats  give  the  disease  to  man. 

The  Pasteur  treatment  for  rabies  is  to  cultivate  the  germs,  so  as  to 


450  SANITATION 

weaken  them,  and  then  to  introduce  the  weakened  germs  into  the 
body.  The  body  develops  germicides  that  kill  not  only  the  weakened 
germs,  but  also  those  that  come  from  an  infection.  The  first  thing  for 
us  to  do,  if  we  have  received  a  wound  from  a  suspected  animal,  is  to  go 
at  once  to  a  physician  to  have  the  wound  disinfected.  The  suspected 
animal  ought  not  to  be  killed,  but  captured,  and  confined  for  about  10 
days.  If  it  remains  well,  it  cannot  have  the  rabies,  and  cannot  give  the 


SCARLET  FEVER 

HERE 

All  Persons  Are  Hereby  Warned 
NOT  To  Remove  This  Placard 

UNDER  PENALTY  OF  THE  LAW 


Fig.  311. 
Quarantines  should  be  respected. 

disease.  If  all  dogs  could  be  muzzled  for  a  few  years,  there  would 
probably  be  no  more  hydrophobia,  for  one  dog  could  not  infect  another. 
So-called  madstones  are  of  no  use  in  curing  the  disease. 

437.  Quarantine. — Quarantine  (Fig.  311)  is  the  isola- 
tion, or  setting  apart,  of  a  person  having  an  infectious 
disease,  so  that  the  disease  may  not  spread  to  the  com- 
munity. Quarantine  is  also  used  in  the  case  of  goods, 
plants,  cattle,  etc.,  if  they  are  suspected  of  infection.  In 
the  case  of  a  ship  coming  to  our  ports,  quarantine  is  the 


QUARANTINE  451 

detaining  of  the  passengers  and  goods  on  board  the  ship 
until  the  health  officials  are  satisfied  that  no  infectious 
diseases  are  being  brought  into  the  country.  In  the  case 
of  a  house,  quarantine  means  the  preventing  of  persons 
from  going  into  the  house,  or  more  especially  from  leaving 
the  house,  for  fear  that  they  may  carry  disease  to  the 
community.  Quarantine  means  "forty,"  and  comes  from 
the  fact  that  governments  of  former  times,  not  knowing 
the  incubation  periods  of  germs,  nor  the  time  during 
which  infections  were  possible,  detained  suspected  trav- 
elers and  goods  for  40  days  before  admitting  them  into  a 
country. 

Do  we  really  understand  what  we  have  learned  about 
the  spreading  of  disease  by  germs?  If  we  do,  we  shall  see 
at  once  how  valuable  and  how  necessary  it  is  for  a  city  to 
be  able  to  quarantine  persons  suffering  from  dangerous 
diseases.  We  shall  also  be  able  to  see  the  value  of  isola- 
tion even  when  it  causes  us  personally  great  inconvenience. 
Suppose  that  we  have  smallpox,  or  that  a  member  of  our 
family  has  it ;  we  ought  still  to  realize  that  the  community 
has  a  right  to  demand  of  us  that  we  prevent  the  disease, 
by  all  the  means  in  our  power,  from  spreading  to  those 
about  us.  If  we  are  recovering  from  scarlet  fever,  we 
know  we  ought  not  to  go  to  school,  nor  to  mingle  with 
other  people,  until  we  are  absolutely  certain  that  the  last 
of  the  "  scaling "  is  over.  We  also  know  that  articles 
such  as  milk  bottles  should  not  be  taken  away  from  a 
house  that  is  quarantined;  they  may  be  infected.  By  the 
mingling  of  infected  milk  bottles  with  those  going  to  other 
houses,  a  whole  neighborhood  may  be  stricken.  Sanitary 
experts  say  that  milk  bottles  should  not  be  left  at  an  in- 


452  SANITATION 

fee  ted  house  at  all,  but  that  the  milkman  should  pour  the 
milk,  out  of  doors,  into  vessels  belonging  to  the  house. 

How  shall  a  person  having  a  dangerous  germ  disease  be  isolated? 
In  some  cases  it  may  be  best  for  him  to  go  to  a  hospital  for  contagious 
diseases;  in  other  cases  he  may  be  left  in  his  own  house,  with  his  nurse, 
but  all  other  persons  may  be  required  to  leave  the  house.  In  some 
cases  only  room  isolation,  or  confinement  in  a  certain  room,  is  advised. 
In  room  isolation  the  cracks  about  the  doors  and  transoms  leading  to 
the  remainder  of  the  house  should  be  closely  sealed,  and  the  nurse 
should  not  mingle  with  the  family.  But  room  isolation  is  usually 
unsatisfactory  and  dangerous,  because  it  is  not  properly  carried  out, 
and  is  not  a  real  isolation.  Real  isolation  in  a  room  is  not  ordinarily 
possible  unless  the  house  is  a  large  one,  and  is  so  arranged  that  the 
patient  and  the  nurse  can  be  removed  to  a  really  separate  part  of  it. 

The  illustrations  already  given  show  us  that  the  real  value  of  isola- 
tion, like  that  of  other  sanitary  measures,  depends  on  how  it  is  carried 
out.  If  we  elect  officers  to  provide  a  good  quarantine,  we  must  support 
them  when  they  are  obliged  to  use  force  with  some  persons  who  refuse 
to  observe  quarantine.  Furthermore,  we  ourselves  must  obey  the 
regulations  of  our  health  department,  not  merely  in  the  letter,  so  that 
we  may  just  escape  punishment,  but  in  the  spirit,  because  we  recognize 
the  fact  that  they  are  for  the  greatest  good  of  all  the  people. 

438.  Disinfection. — We  have  already  learned  (cf. 
§  423)  that  disinfection  means  the  destruction  of  harmful 
germs.  It  applies  to  such  familiar  operations  as  the 
boiling  of  milk  and  water,  the  filtering  of  water,  and  the 
washing  of  hands  and  clothing,  as  well  as  to  the  treatment 
of  a  wound  with  carbolic  acid,  or  the  fumigation  of  a  room 
with  burning  sulphur.  Preservatives  are  disinfectants 
put  into  food  (cf.  §  425). 

The  need  of  careful  disinfection  during  and  after  dis- 
ease is  much  greater  than  people  realize;  because  disin- 


DISINFECTION  453 

fection  is  neglected,  preventable  diseases  continue  to 
attack  mankind.  Some  of  the  methods  of  disinfection 
for  particular  diseases  have  already  been  suggested. 
Thus,  the  sputum  of  a  person  having  consumption  or 
pneumonia  ought  to  be  burned  (cf.  §§  429  and  436);  the 
cloths  containing  the  discharges  from  the  nose  and  throat 
during  scarlet  fever  and  measles  ought  to  be  boiled  in  hot 
water;  dishes  used  by  a  patient,  even  if  he  has  "only  a 
cold/'  ought  to  stand  in  boiling  water  for  some  minutes, 
so  that  the  germs  adhering  to  them  may  be  entirely 
destroyed.  The  need  of  disinfecting  the  body  waste  of 
typhoid  patients  has  not  yet  been  appreciated  sufficiently ; 
it  is  through  these  wastes  that  water  is  polluted,  and  that 
the  disease  is  spread  (cf.  §  427).  Experience  has  taught 
men  that  direct  sunlight  is  an  excellent  germicide,  hence 
they  have,  from  time  immemorial,  hung  clothing  and 
bedding  in  the  sunlight  for  disinfection.  Of  course  a  large 
part  of  the  disinfection  that  is  carried  out  "in  the  open" 
is  due  to  air  (cf.  §  58).  Long-continued  drying  destroys 
germs,  as  it  does  other  living  things.  One  way  in  which 
salt  acts  as  a  preservative  is  that  it  removes  water  from 
the  cells  of  the  germs  that  cause  decay.  Long-continued 
cold  also  destroys  germs ;  strange  as  it  may  seem,  explorers 
in  polar  regions  are  not  troubled  with  colds ;  the  germs  of 
colds  cannot  live  there. 

Substances  having  poisonous  properties  are  also  used  to  destroy 
germs.  One  of  the  most  frequently  used  of  these  chemical  disin- 
fectants is  mercuric  chloride.  This  is  a  compound  of  mercury  and 
chlorine;  it  is  also  known  as  bichloride  of  mercury  and  as  corrosive 
sublimate.  It  may  be  purchased  in  tablets  that  dissolve  readily  in 
water.  The  " strength"  of  the  solution  is  usually  1  part,  by  weight, 


454  SANITATION 

of  mercuric  chloride  to  1,000  parts  of  water.  Common  salt  is  mixed 
with  the  mercuric  chloride  before  the  water  is  added.  The  solution  is 
very  poisonous  if  taken  internally,  but  it  is  very  efficient  in  destroying 
germs  that  are  on  the  hands,  on  washable  clothing,  and  on  floors. 
Mercuric  iodide,  a  compound  of  mercury  and  iodine,  is  an  even  better 
disinfectant  than  mercuric  chloride,  especially  for  surgical  instru- 
ments. It  is  mixed  with  potassium  iodide  to  make  it  soluble.  Its 
ordinary  name  is  biniodide  of  mercury.  Strong  acids  and  alkalies  are 
powerful  disinfectants,  but  they  are  not  used  as  much  as  they  might 
be  because  they  act  upon  skin,  clothing,  etc.  The  most  common  acid 
used  in  natural  disinfection  is  the  hydrochloric  acid  of  the  stomach 
(cf.  §  364).  In  artificial  disinfection  carbolic  acid  is  used.  In  winter, 
carbolic  acid  is  usually  a  solid;  in  summer  it  is  a  thick  liquid.  The 
solid  melts  readily  if  it  is  set  in  a  pan  of  warm  water.  The  carbolic 
acid  disinfecting  solution  contains  2.5  to  5  grams  of  the  acid  in  100 
grams  of  water.  This  would  be  2  to  3  tablespoons  full  of  acid  to  a  pint 
of  water.  The  most  common  base,  or  alkali,  used  in  disinfection  is 
"milk  of  lime"  (cf.  §  132).  Lye  is  also  used.  The  disinfectant  known 
as  chloride  of  lime,  or  "bleaching  powder"  (cf.  §  110),  is  made  by 
passing  chlorine  into  slaked  lime. 

To  disinfect  a  house  by  fumigation,  gaseous  germicides 
are  used.  The  two  most  common  ones  are  sulphur 
dioxide  and  formaldehyde.  The  sulphur  dioxide  is  com- 
monly made  by  the  burning  of  sulphur  "candles."  The 
candles  used  do  not  as  a  rule  give  enough  sulphur  dioxide 
to  destroy  the  germs ;  they  are  also  a  source  of  danger,  for 
they  may  set  the  house  on  fire.  Sulphur  dioxide  gas  can 
be  obtained  more  safely  if  liquid  sulphur  dioxide,  or  the 
solution  of  the  gas,  is  poured  out  in  saucers,  and  allowed 
to  evaporate.  Sulphur  dioxide  is  used  to  destroy  vermin, 
as  well  as  germs.  Formaldehyde  is  a  compound  of  car- 
bon, hydrogen,  and  oxygen  (cf.  §  123) ;  it  is  a  much  better 
germicide  than  sulphur  dioxide.  One  of  the  easiest  ways 


SUMMARY  455 

of  getting  the  gas  into  a  room  is  to  sprinkle  40%  ' '  forma- 
lin "  solution  (a  solution  containing  formaldehyde)  upon 
sheets  placed  in  the  room  to  be  disinfected.  The  sheets 
may  be  hung  upon  clothes  lines.  The  room  should  be 
closed  tightly  for  several  hours  to  give  the  disinfectant 
time  to  complete  its  work.  Separate  articles  may  be 
disinfected  by  placing  them  in  a  trunk,  between  cloths 
wet  with  formalin  solution. 

Many  accidents  occur  every  year  because  some  people 
keep  disinfectants  in  the  family  medicine  closet,  or  have 
them  about  the  house,  without  a  warning  label.  All  such 
substances  should  be  kept  by  themselves,  in  a  locked  case, 
and  should  be  distinctly  marked.  They  should  also  be 
colored  by  the  addition  of  a  tiny  amount  of  some  bright 
dye,  so  that  no  one  will  mistake  them  for  something  else. 


439.  Summary. —  Contagious  diseases  are  caused  by  germs.  Germs 
may  be  bacteria  or  protozoa.  The  science  of  germs  is  bacteriology. 

Hygiene  is  the  science  of  keeping  the  body  in  good  health;  sanita- 
tion deals  especially  with  the  health  of  the  community.. 

Germs  grow  in  the  body  because  they  find  favorable  conditions 
there.  The  body's  defenders  against  germs  that  are  in  the  blood  are 
the  white  corpuscles  and  the  germicides. 

The  effect  of  germs  is  due  to  the  toxins  which  they  produce.  From 
the  time  we  are  exposed  to  a  disease  until  we  "come  down"  with  it,  the 
germs  are  multiplying;  this  is  the  incubation  period. 

Germs  can  be  destroyed,  outside  of  the  body,  by  cleansing  the 
body  and  its  surroundings,  by  removing  dust,  by  letting  light  and  air 
into  our  houses,  and  by  disinfectants. 

Disinfection  is  the  destruction  of  harmful  germs.  Fumigation  is 
disinfection  by  gases. 

Flies  hatch  in  filth,  visit  dirty  places,  and  infect  our  surroundings 
and  our  food.  Houses  should  be  screened  against  them,  those  inside 


456  SANITATION 

houses  should  be  killed,  and  the  neighborhood  should  be  kept  clean,  sa 
that  they  will  not  find  food  or  breeding  places. 

Mosquitoes  hatch  in  water,  and  live  in  damp  places.  One  variety 
carries  malaria  germs,  another  the  germs  of  yellow  fever.  Their 
breeding  places  should  be  destroyed. 

.  Food  should  be  handled  only  with  clean  hands,  and  should  be 
stored  only  in  clean  places.  Tainted  food  should  be  destroyed.  Food 
exposed  to  the  dusty  air  of  a  city  street  will  be  infected. 

Infected  milk  may  spread  consumption,  typhoid  fever,  scarlet  fever, 
etc.  Milk  should  be  kept  cold  in  summer.  If  it  is  suspected  of  in- 
fection, it  should  be  pasteurized. 

Preservatives  are  disinfectants  put  into  food.  They  should  not  be 
used,  as  they  injure  the  body. 

Public  drinking  cups,  money,  public  towels  and  soap,  and  pencils 
that  have  been  in  somebody's  mouth,  are  infected. 

Typhoid  fever  germs  enter  the  body  through  the  digestive  tract, 
and  develop  in  the  small  intestine. 

Tuberculosis  attacks  the  lungs  of  most  people  at  some  time  or  other. 
It  can  be  cured,  if  treated  soon  enough,  by  fresh  air,  sufficient  clothing, 
and  nourishing  food. 

Spitting  in  public  is  dangerous  to  public  health. 

Colds  should  not  be  despised,  but  cured. 

Diphtheria  is  often  scattered  by  a  healthy  person  who  has  the  germs 
in  his  throat,  and  who  infects  milk,  drinking  cups,  dishes,  etc. 

Antitoxins  are  substances  produced  by  the  body  to  neutralize  toxins. 

Smallpox  is  an  eruptive  disease;  it  is  prevented  by  vaccination. 
" Vaccine  virus"  contains  weakened  germs;  these  stimulate  the  body 
to  produce  the  proper  germicide. 

Some  other  germ  diseases  are  scarlet  fever,  measles,  pneumonia, 
yellow  fever,  tetanus,  and  rabies. 

Quarantine  is  the  isolation  of  infected  persons  or  goods;  it  is  neces- 
sary for  public  health. 

Health  regulations  should  be  observed  and  respected. 

Disinfection  destroys  germs  after  a  disease,  so  as  to  prevent  a 
repetition  of  the  disease. 

Chemical  disinfectants  are  corrosive  sublimate,  carbolic  acid,  milk 
of  lime,  chloride  of  lime,  sulphur  dioxide,  formaldehyde,  etc. 


EXERCISES  457 

Disinfectants  should  be  separated  from  medicines,  so  that  they  may 
not  be  swallowed  by  mistake. 

440.     Exercises. 

1.  Give  some  of  the  objections  to  smoke  in  the  air  of  cities. 

2.  If  you  remember  that  plants  and  animals  build  up  complex 
materials  out  of  simple  foods,  what  does  the  work  of  bacteria  and 
ferments  seem  to  be?    What,  then,  is  the  function  of  bacteria  in  the 
economy  of  Nature? 

3.  What  are  the  objections  to  the  making  of  clothing  in  " sweat 
shops"  and  in  houses  where  families  live? 

4.  What  effect  has  the  density  of  the  population  upon  health  and 
the  length  of  life? 

5.  Suggest  how  it  is  possible  that  the  city  may  be  made  more  health- 
ful than  the  country. 

6.  To  what  danger  are  men  exposed  who  work  in  factories  where 
metal  articles  are  ground  or  filed? 

7.  What  is  the  advantage,  to  a  city,  of  a  hospital  for  persons  having 
contagious  diseases?    What  does  your  town  or  community  do  with  its 
smallpox  patients? 

8.  Some  people  contend  that  rats  and  mice,  like  flies,  are  scavengers, 
and  are  therefore  useful  to  man.    Are  they  economical  scavengers  from 
the  community's  point  of  view? 

9.  Suggest  how  a  house  may  be  placed  so  as  to  get  the  greatest 
possible  amount  of  winter  sunshine. 

10.  Give  the  objections  to  having  unlighted  clothes  closets  in  a 
house. 

11.  Medical  books  state  that  the  period  of  isolation  for  scarlet  fever 
should  be  six  weeks;  what  is  the  practice  in  your  community?    Is  it 
possible  for  a  child  in  your  community  to  go  to  school  while  another 
child  in  the  same  house  has  scarlet  fever? 

12.  Ask  a  physician  or  health  officer  about  the  number  of  cases  of 
infectious  diseases  in  your  town  in  the  course  of  a  year.    Can  you  find 
any  reasons  for  the  change  in  number  from  month  to  month? 

13.  Is  inoculation  ever  used  to  protect  animals  from  disease?    Give 
instances. 


458  SANITATION 

14.  In  what  sense  is  the  growing  of  clover,  alfalfa,  etc.,  an  inocula- 
tion of  the  soil?     (Cf.  §  56). 

15.  How  does  the  formation  of  toxins  in  the  soil  resemble  their 
production  in  the  blood? 

16.  If  you  were  planning  to  disinfect  a  room  with  formaldehyde, 
suggest  how  you  would  place  books,  so  that  the  germicide  could  really 
get  at  them;  closets;  bureaus  and  dressers;  bedding;  clothing.     What 
precautions  would  you  take  regarding  cracks  around  doors,  etc.? 

17.  Why  does  a  dilute  sugar  solution,  such  as  a  fruit  sauce,  need  to 
be  so  carefully  sterilized  and  kept  away  from  the  air,  while  a  con- 
centrated sugar  solution,  such  as  a  preserve,  does  not? 

18.  Would  you  say  that  sanitary  housekeeping  is  a  simple  or  a 
complex  problem?    Is  it  worth  while? 


APPENDIX 


TABLE  I.    THE  METRIC  SYSTEM. 

1.  Length.    The  unit  of  length  is  the  meter  (39 . 37  in.). 

10  millimeters  (mm.)  =  1  centimeter  (cm.). 
10  centimeters  =1  decimeter  (dm.). 

10  decimeters  =  1  meter  (m.). 

1,000  meters  =  1  kilometer  (km.). 

Note  that  the  prefix  "milli-"  means  0.001,  as  mi7Z  =  0.001  dollar; 
"centi-"  means  0.01,  as  cent  =  0.01  dollar;  "deci-"  means  0.1,  as 
dime  =  Q.  1  dollaj.  "Kilo-"  means  1,000. 

2.  Square  Measure,  or  Area. 

100  square  millimeters  (sq.  mm.)  =1  sq.  centimeter  (sq.  cm.). 
100  square  centimeters  =  1  sq.  decimeter  (sq.  dm.). 

100  square  decimeters  =1  sq.  meter  (sq.  m.). 

3.  Cubic  Measure,  or  Volume.     The  unit  of  volume  is  the  liter, 

which  is  1  cu.  dm.,  or  1,000  c.c. 

1,000  cubic  millimeters  (cu.  mm.)  =  l  cubic  centimeter  (c.c.). 
1,000  cubic  centimeters  =1  cubic  decimeter  (cu.  dm.). 

1  cubic  decimeter  =1  liter  (1.). 

10  liters  =  1  dekaliter  (dl.). 

10  dekaliters  =1  hectoliter  (hi). 

10  hectoliters  =  1  kiloliter  (kl.). 

4.  Weight.    The  gram  is  the  weight  of  1  c.c.  water  at  4°C.;  1  liter  of 

water  at  4°C.  weighs  1  kilogram. 
10  milligrams  (mg.)  =1  centigram  (eg.). 
10  centigrams  =1  decigram  (dg.). 

10  decigrams  =  1  gram  (g.). 

1,000  grams  =1  kilogram  (kg.). 

1,000  kilograms  =  1  metric  ton. 

459 


460  APPENDIX 

TABLE  II.  EQUIVALENTS. 

1.  Length. 

1  centimeter  =0.3937  in. 

1  meter          =  39 . 37  in.  =  3 . 28  ft. 

1  kilometer    =  1,000  m.  =  0 . 6214  mile. 

1  inch  =2.54  cm. 

Ifoot  =  0.3048m. 

1  mile  =  1 . 6094  km. 

2.  Area. 

1  sq.  cm.          =0. 155  sq.  in. 

1  sq.  m.  =10.764sq.  ft.  =  1.196  sq.  yd. 

100  m.  square  =10,000  sq.  m.  =  l  hectare  =  2. 47  acres. 

1  sq.  km.         =  0 . 385  sq.  mile. 

3.  Volume. 

1  cu.  cm.  =  0.061  cu.  in. 

1  cu.  m.  =35.315cu.  ft. 

1  liter  •    =1,000  cu.  cm.  =  1.0567  qt.  (U.  S.). 

4.  Weight. 

1  gram  =  15. 4324  grains. 

1  kilogram  =  1 ,000  grams  =  2 . 2046  Ibs. 

1  metric  ton  =  1,000  kg.  =  2,204. 6  Ibs. 

1  short,  or  net  ton  =2,000  Ibs. 

1  long,  or  gross  ton  =  2,240  Ibs. 

1  grain  -  0 . 0648  gram. 

1  ounce  (avoirdupois)  =  28 . 35  grams. 

1  ounce  (troy)  =31 . 1  grams. 


APPENDIX 


461 


TABLE  III.    DENSITIES  OF  SOME  SUBSTANCES. 


Acetic  acid*    . 

1.053 

Magnesium     .      . 

1.75 

Alcohol  (ethyl)*  . 

0.794 

Marble      .... 

2.7 

Aluminum       .      .      , 

2.67 

Mercury  (at  0°C.)      . 

13.596 

Brass    

8.3 

Nickel        .... 

8.57 

Carbolic  acid  . 

0.95 

Nitric  acid  (cone.)*   . 

1.42 

Carbon  (charcoal) 

1.6 

Oil  (cotton  seed) 

0.926 

Carbon  (gas)  . 

1.8 

Oil  (linseed)    .      .      . 

0.942 

Carbon  disulphide*   . 

1.27 

Oil  (olive)        .      .      . 

0.918 

Chloroform*    . 

1.5 

Oil  (turpentine)    . 

0.873 

Clay 

1.9 

Phosphorus  (yellow) 

1.83 

Coal  (anthracite) 

1.26  to  1.8 

Platinum  .... 

21.5 

Coal  (soft)       .      .      . 

1.2  to  1.5 

Potassium       .      . 

0.865 

Copper      .... 

8.9 

Sand  (dry)      ... 

1.4 

Cork 

024 

Silver  

10.57 

Diamond  .... 

.  —  •  i 

3.53 

Sodium      .      .  '  . 

0.97 

Ether*       .... 

0.72 

Sulphur     .      .      . 

2.03 

Gasoline    .... 

0.67  . 

Sulphuric  acid  (cone.) 

1.854 

Glass    

2.6  to  3.6 

Tin       ..... 

7.29 

Glycerine  .... 

1.27 

Water  at  0°C.       .      . 

0.999 

Gold     .     ,      . 

19.3 

Water  at  4°C.       .      . 

1.000 

Hydrochloric  acid 

Water  at  100°C.  .      . 

0.958 

(cone.)*       .      .      . 

1.22 

Water  (sea)     .      .      . 

1.026 

Ice       ..... 

0.918 

Wood  (hickory,  dry) 

1.00 

Iodine  .      .      .      ,      . 

4.95 

Wood  (maple,  dry)    . 

0.64 

Iron      

7.8 

Wood  (white  oak,  dry) 

0.86 

Kerosene   .      ... 

0.79 

Wood  (white  pine,  dry) 

0.42     . 

Lead     ..... 

11.35 

Zinc      

6.9  to  7.2 

Limestone       .      . 

3.2 

At  15°  C. 


462 


APPENDIX 


TABLE  IV.    WEIGHT  (IN  GRAMS)  OF  A  LITER  OF  THE 
DRY  GAS  AT  o°C.  AND  760  MM. 


Air        

1.293 

Marsh  gas       .  "  . 

0.717 

Ammonia  .... 

0.762 

Nitric  oxide    . 

1.34 

Carbon  dioxide     .  •  . 

1.977 

Nitrogen    .... 

1.256 

Carbon  monoxide 

1.251 

Nitrous  oxide 

1.97 

Chlorine    .... 

3.18 

Oxygen      .      . 

1.429 

Hydrochloric  acid 

1.61 

Sulphur  dioxide    . 

2.87 

Hydrogen 

0.0896 

Steam  

0.806 

Hydrogen  sulphide    . 

1.542 

TABLE  V.    THE  MELTING  POINTS  OF  SOME  SOLIDS. 


Hydrogen 

-256.5°C. 

Lead     

327° 

Alcohol  (ethyl)     .      . 

-130° 

Zinc      

419° 

Mercury    .... 

-39.5° 

Aluminum 

657°C. 

Ice        

0° 

Salt      

820° 

Olive  oil    .      .      .      . 

3° 

Silver  

961° 

Acetic  acid 

17° 

Copper      .... 

1065° 

Carbolic  acid  . 

43° 

Gold    

1071° 

Paraffin     .... 

55° 

Cast  iron  .... 

1200° 

Sulphur     .... 

114° 

Pure  iron  .... 

1550° 

Sugar  (cane)   .      .      . 

160° 

Platinum  .... 

1775° 

Tin       

232° 

APPENDIX 


463 


TABLE  VI.    BOILING  POINTS  OF  SOME  SUBSTANCES. 


Hydrogen 

252°C. 

Alcohol,  ethyl 

78° 

Liquid  air 

-190° 

Water  

100° 

Acetylene  .... 

-  72° 

Salt  brine  (saturated) 

109° 

Ammonia  .... 

-  33° 

Turpentine 

159° 

Sulphur  dioxide    . 

-     8° 

Carbolic  acid  . 

183° 

Ether   

35° 

Camphor   .... 

205° 

Chloroform      . 

61°C. 

Glycerine  .... 

291° 

Gasoline    .... 

70°  to  90° 

Kerosene   .... 

150°  to  250* 

TABLE  VII.    SPECIFIC  HEATS. 


Aluminum 

0.214 

Magnesium     . 

0.250 

Asbestos    .... 

0.195 

Marble       .... 

0.21 

Brass    

0.089 

Mercury  (solid)    . 

0.0319 

Cadmium  .... 

0.0567 

Paraffin     .... 

0.6939 

Cement      .... 

0.20 

Platinum   .... 

0.0324 

Charcoal    .... 

0.16 

Quartz       .      ... 

0.188    . 

Diamond  .... 

0.459 

Salt      

0.219 

Copper      .      ... 

0.0952 

Silver   

0.057 

Glass    .      .      . 

0.1988 

Sugar   

0.274 

Gold 

0  .  0324 

Sulphur 

0.178 

Granite      .... 

0.192 

Tin 

0  .  0562 

Ice       

0.55 

Zinc      

0.0955 

Iron      

0.114 

464 


APPENDIX 


TABLE  VIII.    VAPOR  PRESSURES  OF  ICE  AND  WATER 
AT  DIFFERENT  TEMPERATURES. 


Temperature 

Pressure  in  Milli- 
meters of  Mercury 

Temperature 

Pressure  in  Milli- 
meters of  Mercury 

-10°C. 

2.0 

29°C. 

29.8 

-  5° 

3.0 

30° 

31.6 

0° 

4.6 

31° 

33.4 

10° 

9.2 

32° 

35.4 

11° 

9.8 

33° 

37.4 

12° 

10.5 

40° 

55.0 

13° 

11.2 

50° 

92.2 

14° 

11.9 

60° 

149.2 

15 

12.7 

70° 

233.8 

16° 

13.6 

80° 

355.5 

17° 

14.5 

90° 

526.0 

18° 

15.4 

99° 

733.2 

19° 

16.4 

99.5° 

746.5 

20° 

17.4 

100.0° 

760.0 

21° 

18.5 

111.7° 

1,140 

22° 

19.7 

120.6° 

1,520 

23° 

20.9 

133  .  9° 

2,280 

24° 

22.2 

159.2° 

4,560 

25° 

23.5 

180.3° 

7,600 

26° 

25.0 

201.9° 

12,160 

27° 

26.5 

213  .  0° 

15,200 

28° 

28.1 

224.7° 

19,000 

APPENDIX 


465 


TABLE  IX.    THE  ELEMENTS  AND  THEIR  SYMBOLS. 


Aluminum 
Antimony 

Al 
Sb 

Molybdenum        .      .      . 
Neodymium 

Mo 

Nd 

Argon  . 

.     .                A 

Neon 

Ne 

Arsenic 

....     As 

Nickel 

Ni 

Barium 

.      .      .      .     Ba 

Niton  (radium  emanation) 

Nt 

Bismuth    . 

.      .      .      .     Bi 

Nitrogen         

N 

Boron 

B 

Osmium 

Os 

Bromine 

Br 

Oxvcen 

o 

Cadmium 
Caesium 

.      .      .      .     Cd 
Cs 

Palladium       
Phosphorus 

Pd 
p 

Calcium 

.      .      .      .     Ca 

Platinum 

Pt 

Carbon 
Cerium 
Chlorine 

.      .      .      .     C 
.      .      .      .     Ce 
.      .      .      .     Cl 

Potassium       
Praseodymium     .... 
Radium     

K 
Pr 
R* 

C  hromium 

Cr 

Rhodium 

Rh 

Cobalt 

Co 

Rubidium 

Rb 

Columbium 

Cb 

Ruthenium 

Ru 

Copper 

Cu 

Samarium 

Sm 

Dysprosium 

Dy 

Scandium 

So 

Erbium 

Er 

Selenium                .... 

Se 

Europium 

.      .      .      .     Eu 

Silicon        

Si 

Fluorine     . 
G  adolinium 

.....     F 
Gd 

Silver  
Sodium 

Ag 

Na 

Gallium 

Ga 

Strontium 

Sr 

Germanium 

Ge 

Sulphur 

g 

Glucinum 

.      .      .      .     Gl 

Tantalum 

Ta 

Gold           .      . 

.      .      .      .     Au 

Tellurium        

Te 

Helium 

.      .      .      .     He 

Terbium    

Tr 

Hydrogen 

.     .     .     .     H 

Thallium   

T1 

Indium 

In 

Thorium 

Th 

Iodine 

I 

Thulium 

Tm 

Iridium 

Ir 

Tin                              .      . 

Sn 

Iron 

.      .      .      .     Fe 

Titanium               .... 

Ti 

Krypton    . 

.      .      .      .     Kr 

Tungsten         

W 

Lanthanum 

La 

Uranium 

Ur 

Lead 

Pb 

Vanadium 

v 

Lithium 

Li 

Xenon 

Xe 

Lutecium         . 

Lu 

Ytterbium 

Yb 

M  agnesium 

.      .      .     Mg 

Yttrium 

Y 

Manganese 

.      .      .      .     Mn 

Zinc           

7,n 

Mercury    . 

.      .      .      .     Hg 

Zirconium       .      .      .   ,  . 

Zr 

466 


APPENDIX 


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•sapixoipAjj 


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•saptu'BXoo.uaj 


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s 

<!<j^fflfflOOOOOOMfefe^gggg^;pLlcZM^KMN 


APPENDIX 


467 


TABLE  XI.    HARDNESS  OF  SUBSTANCES. 

We  can  compare  the  hardness  of  two  bodies  by  rubbing  them 
together;  the  one  having  the  greater  hardness  scratches  or  indents 
the  other.  In  the  scale  of  hardness  bodies  usually  have  positions 
between  1  and  10.  The  diamond  is  the  only  substance  of  hardness 
10  (tf-  §  119).  Substances  that  can  be  indented  by  the  finger  nail 
have  a  hardness  of  less  than  1 .  A  substance  of  hardness  6.5  is  scratched 
by  a  substance  of  hardness  7,  but  scratches  a  substance  of  hardness  6. 
The  list  below  is  taken  from  the  Smithsonian  Tables,  as  they  are  given 
in  the  "Handbook  of  Chemistry  and  Physics,"  published  by  the 
Chemical  Rubber  Company,  Cleveland,  Ohio. 


Substance 

Hardness 

Substance 

Hardness 

Talc      .            ... 
Rock  salt        .      .      . 
Calcite 
Fluorite 

1 

2 
3 

4 

Flint     .      .      .      .      . 
Galena.      .      . 
Garnet       .... 
Glass    

7 
2.5 
7 
4  5  to  6  5 

Apatite 
Feldspar 
Quartz 
Topaz 

5 
6 

7 
8 

Gold     
Graphite    .... 
Gypsum    .... 
Hematite 

2  .  5  to  3 
0  .  5  to  1 
1.6  to  2 
6 

Corundum 
Diamond 

9 
10 

Hornblende     . 
Iron 

5.5 

4  to  5 

i 

Agate 

7 

Lead     .... 

1  5 

Alabaster  .... 
Alum    .                  . 
Aluminum 
Amber 
Anthracite 
Antimony 
Asbestos    . 
Asphalt      .            .      . 
Barite 

1.7 
2  to  2.  5 
2 
2  to  2.5 
2.2 
3.3 
5 
1  to  2 
3  3 

Magnetite 
Marble       .... 
Mica    
Opal     
Orthoclase 
Platinum  .... 
Pyrite  
Silver  
Steel     

6 
3  to  4 
2.8 
4  to  6 
6 
4.3 
6.3 
2.5  to  3 
5  to  8  5 

Bell  Metal            .      . 
Beryl    .      . 
Bismuth    . 
Brass    .                  . 
Copper      .            .      . 
Dolomite  .            .      . 

4 
7.8 
2.5 
3  to  4 
2.5  to  3 
3.  5  to  4 

Stibnite     .... 
Sulphur     .... 
Tin       
Tourmaline 
Wax  (0°C.)      .      .      . 
Zinc      

2 

1.5to2.5 
1.5 
7.3 
0.2 
2.5 

468 


APPENDIX 


TABLE  XH.    PERCENTAGE  COMPOSITION  OF  FOOD 
MATERIALS. 


Food 

Water 

Proteid 

Fat 

Carbo- 
hydrates 

Minerals 

Value  of 
1  Ib.  in 
Large 
Calories 

Apples     .... 

83.2 

0.2 

0.4 

15.9 

0.3 

315 

Beans  (dry)  . 

12.6 

23.1 

2.0 

59.2 

3.1 

1,615 

Beef  (round) 

68.2 

20.5 

10.1 

.... 

1.2 

805 

Beef  (sirloin) 

60.0 

18.5 

20.5 

1.0 

1,200 

Bread      .... 

35.3 

9.2 

1.3 

53.1 

1.1 

1,215 

Butter     .... 

10.5 

1.0 

85.0 

0.5 

3.0 

3,410 

Candy     .... 

3.0 

.... 

.... 

96.5 

0.5 

1,785 

Cheese     .... 

30.2 

28.3 

35.5 

1.8 

4.2 

2,070 

Chicken  .... 

72.2 

24.4 

2.0 

1.4 

540 

Cornmeal 

15.0 

9.2 

3.8 

70.6 

1.4 

1,645 

Eggs  . 

73.8 

14.9 

10.5 

0.8 

721 

Fish  (salmon)     . 

63.6 

21.6 

13.4 

.... 

1.4 

965 

Milk  

87.0 

3.6 

4.0 

4.7 

0.7 

325 

Mutton  (leg)      .      . 

61.8 

18.3 

19.0 

0.9 

1,140 

Oatmeal  .... 

7.6 

15.1 

7.1 

68.2 

2.0 

1,850 

Oysters    .... 

87.1 

6.0 

1.2 

3.7 

2.0 

230 

Peanuts  .... 

9.2 

25.8 

38.6 

24.4 

2.0 

2,560 

Pork  (fresh)        .      . 

52.0 

16.9 

30.1 



1.0 

1,600 

Potatoes  (white) 

78.3 

2.2 

0.1 

18.4 

1.0 

385 

Potatoes  (sweet) 

69.0 

1.3 

0.6 

28.3 

0.8 

480 

Rice  

12.0 

8.0 

2.0 

77.0 

1.0 

1,700 

Strawberries 

90.4 

1.0 

0.6 

7.4 

0.6 

180 

Sugar       .... 

100.0 

•  . 

1,850 

Tomatoes 

95.3 

0.8 

0.4 

3.2 

0.3 

80 

Walnuts  (English)  . 

2.8 

16.7 

64.4 

14.8 

1.3 

3,305 

GLOSSARY 


abdomen 

(ab-do'-men) 

canine 

(ka-nin') 

acetylene 

(a-set'-i-len) 

capillary 

(kap'-il-a-ri) 

adenoids 

(ad'-e-noid) 

carnivorous 

(kar-niv'-o-rus) 

adventitious 

(ad'-ven-tish'-us) 

cartilage 

(kar'-ti-laj) 

afferent 

(af'-er-ent) 

casein 

(ka'-se-m) 

albumin 

(al-bu'-mm) 

centimeter 

(sen'-ti-me-ter) 

alga 

(al'-ga) 

centrifugal 

(sen-trif'-u-gal) 

ambergris 

(am'-ber-gres) 

cerebellum 

(ser'-e-beT-um) 

ameba 

(a-me'-ba) 

cerebrum 

(ser'-e-brum) 

amorphous 

(a-mor'-fus) 

chloride 

(klo'-rid) 

amylopsin 

(am'-y-lop'-sin) 

chlorine 

(klo'-rin) 

aniline 

(an'-i-lm) 

chlorophyll 

(klo'-ro-fil) 

antitoxin 

(an'-ti-tox'-m) 

chrysalis 

(kris-a-lis) 

aorta 

(a-6r'-ta) 

chyle 

(kil) 

aqueducts 

(ak'-we-dukt) 

chyme 

(kirn) 

aqueous 

(ak'we-us) 

cilia 

(sil'-I-a) 

avoirdupois 

(av'-er-du-poiz') 

clavicle 

(klav'-i-k'l) 

axillary 

(ax'-il-la-ri) 

coagulate 

(ko-ag'-u-lat) 

bacilli 

(ba-sil'-i)  ' 

coccyx 

(kok'-six) 

bacteria 

(bak-te'-ri-a) 

cochineal 

(koch'-i-nel) 

barometer 

(ba-rom'-e-ter) 

cocoon 

(ko-koon') 

Bell,    Alexander    Graham.     Born 

composite 

(kom-poz'-It) 

1847.    Inventor  of  the  telephone. 

conifer 

(ko'-ni-fer) 

biceps 

(bi'-seps) 

conjunctiva 

(kon'-junk-ti'va) 

bicuspids 

(bi-kus'-pids) 

contagious 

(kon-ta'-jus) 

bilateral 

(bi-lat'-er-al) 

corolla 

(ko-r6T-a) 

biniodide 

(bm-i'-od-id) 

corpuscle 

(kor'-piis'l) 

bronchi 

(bron'-ki) 

cotyledon 

(kot'-i-le'-dun) 

buoyant 

(boi'-ant) 

Crustacea 

(krus-ta'-she-a) 

cactus 

(kak'-tus) 

crystalline 

(kris'-tal-m) 

caisson 

(ka'-son) 

deciduous 

(de-sid'-u-iis) 

calorie 

(kal'-o-ri) 

decimeter 

(des'-i-me'ter) 

calorimeter 

(kal'-o-rim'-e-ter) 

dendrite 

(den'-drit) 

calyx 

(ka'-lix) 

dentine 

(den'-tm) 

469 

470 


GLOSSARY 


Dewar  (du'-er)  Sir  James.    Scottish 
chemist  who  liquefied  gases,  espe- 
cially hydrogen.     Born  1842. 
diaphragm         (di'-a-fram) 
dietetics  (di-e-tet'-iks) 

diphtheria         (dif-the'-ri-a) 
dirigible  (dir'-i-ji-b'l) 

dynamo  (di'-na-mo) 

efferent  (ef'-er-ent) 

effervesce          (ef-er-ves') 
electrolysis        (e-lek-trol'-i-sis) 
embryo  (em'-bri-6) 

enamel  (en-am'-el) 

environment     (en-vi'-run-ment) 
enzyme  (en'-zim) 

epidemic  (ep'-i-dem'-ik) 

epidermis          (ep'-i-der'-mis) 
epithelial  (ep'-i-the'-li-al) 

esophagus         (e-sof'-a-gus) 
fibrinogen          (fi-brin'-o-gen) 
formaldehyde  (f6r-mal'-de-hid) 
Franklin,  Benjamin.    American  in- 
vestigator,      philosopher,       and 
statesman;  1706  to  1790. 
Galileo  (gal'-i-le'-o).       Italian     as- 
tronomer and  physicist;  1564  to 
1642. 

Galvani  (gal-va'ne).      Italian;    one 
of    the    discoverers    of    current 
electricity.     Lived  1737  to  1798. 
ganglia  (gan'-gli-a) 

gelatine  (jeT-a-tin) 

germicide          (jerm'-i-sid) 
glycogen  (gli'-co-jen) 

gymnosperm     (jim'-no-sperm) 
Gray,  Elisha.    American  electrician, 
and   inventor  of  the  telephone; 
1835-1901. 

Harvey,  William.     English   physi- 
cian who  discovered  the  circula- 


tion of  the  blood.    Lived  1578  to 
1657. 

hemoglobin       (he'-mo-glo'-bm) 
hepatica  (he-pat'-i-ka) 

herbivorous      (her-biv'-o-rus) 
hibernate          (hi'-ber-nat) 
humerus  (hu'-mer-us) 

hydroxide          (hi-drox'-id) 
hygiene  (hi'-ji-en) 

hyoid  (hi'-oid) 

hypocotyl  (hi'-po-cot'-il ) 

immune  (i-mun') 

incisor  (in-sl'ser) 

incubation         (in'-kQ-ba'-shiin) 
inertia  (in-er'-shi-a) 

inoculation        (in-6k'u-la'-shun) 
insulator  (m'sQ-la'-ter) 

intestine  (m-tes'-tm) 

invertase  (in-vert'-as) 

isolation  (I'-so-la'-shun) 

Jenner,  Edward,  M.D.  Born  1749 ; 
died  1823.  English  investigator 
and  physician.  Discoverer  of 
vaccination. 

kilometer          (kil'-o-me'-ter) 
lacteal  (lak'-te-al) 

la  grippe  (la  grip') 

larvae  (lar'-ve) 

Lavoisier    (la'-vwa'-zya/),  Antoine 
Laurent.     French  chemist;  1743 
to  1794.    Proved  that  burning  in 
air  is  union  with  oxygen, 
leaven  (lev'-en) 

legume  (leg'-um) 

Leyden  (H'-den) 

lichen  (li'-ken) 

Liebig  (le'-bik;  German  "k"  is 
softer  than  in  English)  Justus, 
Baron  von.  German  chemist, 
1803  to  1873. 


GLOSSARY 


471 


lymphatic          (lim-fat'-ik) 
medulla  oblongata 

(me-dul'-a  ob'-lon-gah'ta) 
membranous  croup 

(mem'-bra-nus  krup) 
meniscus  (me-nis'-kiis) 

metatarsal         (met'-a-tar'-sal) 
microbe  (mi'-krob) 

millimeter         (mil'-i-fne'-ter) 
monocotyl         (mon'-o-cot'-il) 
Morse,   Samuel  F.  B.     American 
artist  and  inventor.     Lived  1791 
to  1872.    Invented  the  telegraph, 
mucous  (mu'-kus) 

muriatic  (mQr'-i-at'ik) 

myosin  (mi'6-sin) 

Newton,  Sir  Isaac.  English  philoso- 
pher, and  investigator  in  physics 
and  mathematics.  Lived  1642 
to  1727.  Professor  of  mathemat- 
ics at  Cambridge  University, 
England. 

nucleus  (nu'-kle-us) 

octopus  (ok'-to-pus) 

olfactory  (61-fak'-to-ri) 

omnivorous       (om-niv'-o-rus) 
opossum  (o-pos'-um) 

oxide  (6x'-id) 

palate  (pal'-at) 

pancreas  (pan'-kre-as) 

pancreatic         (pan'-kre-at'-ik) 
papilla  (pa-pil'-a) 

paramecium      (par'-a-me'-shi-um) 
Pasteur  (pas'-tur')  Louis.  Lived  1822 
to  1895.    First  a  chemist,  then  a 
founder  of  bacteriology.     Direc- 
tor of  the  Pasteur  Institute,  Paris, 
patella  (pa-teT-a) 

penumbra          (pe-num'-bra) 
perennial  (per-en'-i-al) 


periosteum        (per'-i-os'-te-um) 

petiole  (pet'-i-ol) 

phalanges          (fa-Ian'-  jez) 

pharynx  (far'-inks) 

phenomena       (fe-nom'-e-na) 

phosphorus       (fos'-for-us) 

photometer       (fo-tom'-e-ter) 

pistillate  (pis'-ti-lat) 

planets.  The  planets  are  heavenly 
bodies  that  revolve  about  the  sun. 
Moons  are  secondary  planets  that 
revolve  about  the  planets,  and 
with  them  revolve  about  the  sun. 
The  major  planets  are  Mercury, 
Venus,  Earth,  Mars,  Jupiter, 
Saturn,  Uranus,  and  Neptune. 
The  mean  distance  from  the  earth 
to  the  sun  is  93,100,000  miles. 
The  distance  of  Mercury  is  about 
0.39  of  the  earth's  distance;  that 
of  Venus,  about  0.72;  that  of 
Mars,  about  1.52;  of  Jupiter,  5.2; 
of  Saturn,  9.54;  of  Uranus,  19.2; 
of  Neptune,  30.  The  "year,"  or 
time  of  revolution  about  the  sun, 
is  about  88  days  for  Mercury,  225 
days  for  Venus,  687  days  for 
Mars,  almost  12  years  for  Jupiter, 
and  almost  165  years  for  Neptune. 

pleura  (plu'-ra) 

plumule  (ploo'-mul) 

pneumatic         (nu-mat'-ik) 

Polaris  (po-la'-ris) 

polyp  (pol'-ip) 

posterior  (pos-te'-ri-er) 

Priestley,  Joseph.  English  writer, 
clergyman,  and  chemist.  Lived 
1733  to  1804.  Discovered  oxygen 
Aug.  1,  1774. 

proboscis  (pro-bos'is) 


472 


GLOSSARY 


proteid 

(pro'-te-id) 

stomata             (sto'-ma-ta) 

proteose 

(pro'-te-os) 

strychnine         (strik'-nm) 

protoplasm 

(pro'-to-plazm) 

sublimate          (sub'-li-mat) 

pulmonary 

(pul'-mo-na-ri) 

thermometer     (ther-mom'-e-ter) 

puparium 

(pu-pa'-ri-um) 

Torricelli         (tor-ri-tchell'-y         or 

pylorus 

(pMo'-rus) 

tor'-re-chel'-le).      Italian    physi- 

pyrometer 

(pi-rom'-e-ter) 

cist;  inventor  of  the  barometer. 

python 

(pl'-thon) 

Lived  1608  to  1647. 

quarantine 

(kwor'-an-ten) 

trachea              (tra'-ke-a) 

retort 

(re-tort') 

trichinae            (tri-kl'-ne) 

salicylic 

(sal'-i-sil'-ik) 

trypsin               (trip'-sm) 

salivary 

(sal'-i-va-ri) 

tuberculosis      (tu-bAr'-ku-los'-is) 

saponify 

(sa-pon'-i-fl) 

tympanum        (tim'-pan-um) 

saprophyte 

(sap'-ro-fit) 

urea                   (u'-re-a) 

sebaceous 

(se-ba'-shiis) 

vaccmation       (vak'-si-na'-shun) 

secrete 

(se-kref) 

vacuum             (vak'-u-iim) 

sepal 

(se'-pal) 

vertebra            (ver'-te-bra) 

sepia 

(se'-pi-a) 

villi                    (vil'-I) 

silica 

(sil'-i-ka) 

vitreous             (vit're-us) 

siphon 

(si'-fon) 

vitriol                 (vit'-ri-61) 

solute 

(so-luf) 

Volta  (v6r-ta),  Alessandro,  Count. 

species 

(spe'-shez) 

Italian  physicist  and  discoverer 

spectrum 

(spek'-trum) 

of  electric  currents;  1745  to  1827. 

spirogyra 

(spi'ro-ji'-ra) 

vorticella           (v6r'-ti-ceT-a) 

sputum 

(spu'-tum) 

Watt,   James.     Scottish   inventor; 

stalactite 

(sta-lak'-tlt) 

1736   to    1819.      He   first    made 

stalagmite 

(sta-lag'-mlt) 

instruments  at  the  University  of 

stamen 

(sta'-men) 

Glasgow,  and  then  invented  the 

staminate 

(stam'-i-nat) 

modern  form  of  the  steam  engine. 

steapsin 

(ste-ap'-sm) 

whorl                 (hwurl) 

stipule 

(stip'-ul) 

zymase              (zi'-mas) 

INDEX 

(NUMBERS  DENOTE  PAGES) 


Abdomen,  338,  401 

Absorption  of  light,  155,  162 

Acetic  acid,  116,  117,  189 

Acetylene,  114,  142,  227 

Acids,  98,  188,  189,  454 

Acids,  action  on  carbonates,  119, 191 

action  on  metals,  190 

and  coloring  matter,  190 
Acids,  classes  of,  189 

Acetic,  116,  117,  189 

Butyric,  361 

Carbonic,  117,  265 

Citric,  189 

Hydrochloric,  95,  96,  98,  99,  105 

Inorganic,  189 

Lactic,  189 

Malic,  189 

Nitric,  189,  190 

Oleic,  361 

Organic,  189 

Phosphoric,  189 

Prussic,  116 

Pyrogallic,  166 

Sulphuric,  95,  189 

Tartaric,  116,  189 

Uric,  366 

Acid  reaction,  190,  357 
Adhesion,  28 
Aeration  of  water,  81 
Aeroplane,  184 
Afferent  nerve,  397,  400,  404 
Air,  4,  21,  38,  39,  46,  56,  64,  72,  81, 
98,  232,  233,  234,  429 

a  non-conductor,  72 

brake,  44 

drainage,  237 

in  soil,  270 
Airship,  184 
Albumins,  55,  348 
Alcohol,  56,  116,  119,  188,  355,  388, 
406 


Algae,  301 

Alimentary  canal,  350 

Alkalies,  188,  192,  454 

Alkaline  reaction,  192,  352,  357,  361 

Alloy,  8 

Alluvial  soil,  270 

Alum,  90 

Amber,  130 

Ameba,  313,  339,  377 

Ammonia,  105,  117,  279 

water,  192,  201 
Ammonium  chloride,  54,  105 

hydroxide,  192 

salts,  tests  for,  196 
Amorphous  substances,  91 
Amphibians,  326 
Amylopsin,  360,  361 
Anemometer,  245 
Aneroid  barometer,  233 
Angiosperms,  306 
Aniline,  116 
Animalcule,  314 
Animals,  52,  312,  332 
Anopheles,  426 
Anther,  298 
Anthracite  coal,  262 
Antitoxins,  443 
Appendix,  358 
Aqueous  humor,  416 
Arc  light,  141 
Argon,  54 
Artery,  372,  374 
Artificial  lighting,  223 
Artificial  rocks,  259 
Assimilation,  361 
Atmosphere,  38,  41,  56,  232,  234 
Auricle,  373 
Axil,  290,  295 
Axon,  396 


Backbone,  343 


473 


474 


INDEX 


Bacteria,  55,  57,  76,  81,  203 

and  disease,  425 

in  soil,  279 
Bacteriology,  426 
Baking  powder,  120 
Balances,  11,  176 
Ball-and-socket  joint,  342 
Balloons,  41,  99 
Barnacles,  320 
Barometer,  39,  233,  249 
Basalt,  261 
Bases,  105,  192,  454 
Battery,  137 
Bean,  284 
Bed  rock,  258 

Bell,  Alexander  Graham,  171 
Bell,  electric,  140 
Bell  jar,  47 
Benzene,  114 

Bichloride  of  mercury,  453 
Bile,  358 
Birds,  329 
Bivalves,  320 
Black  lead,  110,  142 
Blacksmith's  forge,  113 
Bladder,  379 
Blast  furnace,  112 
Bleaching  powder,  104 
Blood,  361,  372,  377,  381 

circulation,  372 
Blue  Vitriol,  90 
Boat,  submarine,  44 
Body,  1,  5 
Body  circulation,  373 

human,  338 
Boiler  scale,  79 
Boiling  point,  86 
Bones,  122,  340,  341 
Borax,  201 
Brain,  398 
Bread,  120 
Bright's  disease,  379 
Brimstone,  106 

(see  Sulphur) 
Bronchial  tubes,  384,  385 
Buds,  294 
Bulb,  398,  399 
Bulbs,  296 
Bunsen  burner,  213 


Buoyant  force,  33 
Bureau  of  Standards,  13 
Burner,  Bunsen,  213 
Burner,  central  draft,  224 
Burning,  39,  46 

glass,  159 
Butyric  acid,  361 

Caissons,  44 
Calcium  carbide,  142 

carbonate,  118,  121,  195,  201 

chloride,  191 

hydroxide,  192,  194 

in  soil,  275 

salts,  tests  for,  196 
Calorie,  62,  66,  364 
Calorimeter,  69 
Calyx,  297 
Camera,  166 
Camera,  pin-hole,  151 
Candle,  49,  223,  224 

power,  154 
Capillaries,  372,  376 
Capillary  action,  30,  49 
Carbohydrates,  347 
Carbolic  acid,  454 
Carbon,  110 

dioxide,  51,  94,  117,  118,  119,  120 

disulphide,  106 
Carbonates,  tests  for,  195 
Carbon  in  soil,  275 
Carbonic  acid,  117,  265 
Carborundum,  142 
Carpals,  344 
Carpels,  297 
Cartilage,  340 
Cartridge,  22 
Casein,  88,  348 
Casting  of  metals,  67 
Caustic  potash,  192 

soda,  103,  192 
Caves,  limestone,  122 
Cavendish,  Henry,  96 
Cell,  313 

Cells  and  tissues,  339 
Cells,  electric,  136,  137 
Cellulose,  116 
Center  of  mass,  34 
Centigrade  scale,  61 


INDEX 


475 


Centrifugal  force,  27 
Cerebrum,  398 
Charcoal,  51,  112 
Charring,  110 
Chemical,  changes,  94,  362 

engine,  120 
China,  260 

Chlorides,  tests  for,  195 
Chlorine,  103,  104 

in  soil,  275 

Chlorophyll,  104,  164,  286 
Chrysalis,  323 
Chyle,  358 
Cigarettes,  387,  408 
Cilia,  303,  384 
Ciliary  muscles,  418 
Circuit,  96,  137 
Circulation,  of  air,  218 

of  blood,  372 
Citric  acid,  189 
Clam,  319 
Clavicles,  343 
Climate,  232 
Clothing,  71,  197,  201 
Clouds,  237,  238 
Cloudbursts,  240 
Coagulation,  378 

filters,  82 
Coal,  110 
Coal  tar,  117 
Cohesion,  28,  65 
Coke,  115 
Colds,  387,  442 
Cold  storage,  85 
Collision,  a  source  of  heat,  73 
Color,  162 

Coloring  matter,  190 
Combustion,  48 
Compass,  125 
Composition  of  water,  95 
Compounds,  95,  96 
Compression  of  gases,  68 
Concave,  30 
Concrete,  260 
Conduction  of  heat,  63 
Conductors,  131 
Conglomerate,  259 
Conifers,  306,  308 
Connective  tissue,  340 


Convection,  63,  215,  220 

Convex,  29 

Coral,  122 

Core  of  earth,  38 

Corn,  277 

Cornea,  417 

Corolla,  297 

Corpuscles,  313,  377,  410,  427 

Corrosion  of  metals,  190 

Cortex,  291 

Cotton,  116,  201 

Cotyledons,  284 

Crabs,  320 

Cranium,  342 

Crayfishes,  320 

Crearn,  88 

Crops,  277 

Crust  of  earth,  38,  258 

Crustaceans,  320 

Crystalline  lens,  416 

Crystals,  66,  89 

Cultivating,  272 

Current,  electric,  136 

Currents  and  magnetism,  138 

Curvature,  418 

Cyclones,  246 

Cylinder,  23,  42 

Dairying,  277 
Daniell's  cell,  137 
Davy,  Sir  Humphrey,  114 
Daylight,  158 
Decay,  39 
Delta,  267 
Dendrites,  396 
Density,  31,  32 

of  air,  233 
Dermis,  388 
Detritus,  264 
Dextrose,  349 
Dew,  236 
Dewar  bulbs,  56 
Dew  point,  237 
Diamond,  110 
Diaphragm,  338,  382 
Dicotyl,  285,  291 
Diet,  363 
Dietetics,  363 
Diffraction  of  light,  163 


476 


INDEX 


Diffused  light,  158 

Diffusion  of  gases,  100 

Diffusion  of  liquids,  101 

Digestion,  94,  350,  361,  362,  376 

Dikes,  263 

Diphtheria,  443 

Dipping  needle,  129 

Disc  plows,  273 

Discharge  of  electricity,  132 

Disease,  425,  426,  447 

Disinfection,  429,  452 

Dislocation,  346 

Dispersed  light,  155 

Distillation,  80,  87,  115 

Diving  bells,  44 

Drainage,  270,  276 

Drift,  266 

Drinking  water,  77 

Drop,  29 

Drouth,  271 

Drugs,  367 

Dry  cell,  138 

Dry  distillation,  116 

Dust,  atmospheric,  163 

Dyes,  117,  202 

Dynamo,  143 

Ear,  413 

Earth's  crust,  258 
Earthenware,  260 
Earthshine,  158 
Earthworm,  217 
Echoes,  169 
Eclipse,  3,  153 
Economic  plants,  307 
Efferent  nerve,  397,  400,  404 
Effervescence,  118,  191 
Electric  bell,  140 
Electric  charges,  130,  131 

currents,  136 

furnace,  141 

meter,  228 

motors,  145 

power,  145 

stoves  and  heaters,  214 
Electrical  resistance,  73 
Electrics,  130 
Electrolysis,  95 
Electromagnets,  138 


Electroplating,  142 
Elements,  97 

in  soil,  275 

Elements,  number  of,  107 
Embryo,  282,  284,  298 
Emulsion,  88,  361 
Endosperm,  285 
Energy,  24 
Enzyme,  352 
Epidermis,  388,  391 

of  leaf,  286 

of  stem,  291 

Epiglottis,  353,  354,  384 
Erosion,  268 
Esophagus,  354 
Etching,  191 
Ether,  116 

Eustachian  tube,  414 
Evergreens,  305 
Excretion,  379,  391 
Expiration,  381,  382 
Explosives,  22,  54 
Eye,  415,  416 

Fats,  116,  198,  223,  347,  358,  361, 

363 

Feldspar,  259,  261,  265 
Femur,  344 
Ferment,  352,  356 
Fermentation,  119,  188,  303 
Ferns,  301,  304 
Fertility,  274,  275,  276 
Fertilizers,  55,  278 
Fibrin,  378 
Fibula,  344 
Filament,  298,  302 
Filtering,  81,  82 
Fire,  39,  46 
Fire-damp,  114 

engine,  43 

Fire,  kindling  a,  210 
Fireplace,  211 
Fishes,  324 
Flame,  48 
Flashing  point,  115 
Floating  body,  34 
Floods,  250 
Flowers,  297,  301,  306 
Fly,  322,  429 


INDEX 


477 


Focus,  46,  159 

Fogs,  86,  237 

Food,  347,  353,  361,  363,  366,  431 

and  body  heat,  71 
Foot,  7 
Force,  21,  24 

centrifugal,  27 

buoyant,  33 
Forest,  275,  307 
Formaldehyde,  454 
Fossils,  259 

Franklin,  Benjamin,  133 
Freezing  mixtures,  89 
Friction,  24,  182 

electric  charges  by,  130 

and  heat,  73 
Frog,  327 
Frost,  91,  236 
Fruits,  299,  307 
Fuels,  72 
Fumigation,  429 
Fungi,  301,  303 
Furnace,  hot  air,  64 
Fuse,  228 

Galileo,  20,  39 
Gall,  358 
Galvani,  136 
Gang  plows,  273 
Ganglia,  397 
Gas,  carbon,  112 

illuminating,  225 

for  lighting,  224 
Gases,  54,  68 

collection  of,  45 

expanding,  22 

liquefying  of,  68 

properties  of,  67 
Gas  meter,  226 
Gasoline,  115,  214 

engine,  23 

and  kerosene  stoves,  213 
Gas-pipes  and  fixtures,  225,  226 
Gastric  juice,  189,  351,  356 
Germs,  303,  428,  437,  447 
Gills,  52,  319,  325 
Glacial  drift,  268 

period,  268 

soil,  270 


Glands,  350,  357,  376,  417 
Glass,  43,  221,  222,  223 
Glucose,  349 
Gluten,  348 
Glycerine,  199,  366 
Glycogen,  358,  362 
Granite,  259,  261,  263 
Graphite,  5,  110,  142 
Gravitation,  18 
Gravity,  17,  18,  22,  29,  268 
Gravity  cell,  137 
Gray,  Elisha,  171 
Gun  cotton,  54 
Gunpowder,  22,  54,  210 
Gymnosperms,  291,  305 
Gypsum,  279 

Habit,  405 
Hail,  240 
Hair,  389 
Halo,  161 

Hardness  of  water,  79 
Harvey,  372 
Hearing,  409,  413 
Heart,  373,  374 
Heat,  52,  59,  62,  136 

capacity,  70 

sources  of,  72 

use  of,  by  the  body,  71,  347 
Heating,  214 

of  air,  234 

hot  water  and  steam,  214 

systems,  220 
Hemoglobin,  377 
Hinge  joint,  341 
Hornblende,  259 
Horse-power,  25 
Human  body,  338 
Humerus,  344 
Humidity,  220,  221,  236 
Humor,  aqueous,  416 
Humus,  269 
Hunger,  410 
Hurricanes,  249 
Hydra,  314 

Hydrants  and  traps,  209 
Hydrocarbons,  114 
Hydrochloric  acid,  105,  189 
Hydrogen,  95,  96,  98,  99,  103 


478 


INDEX 


Hydrogen  in  soil,  275 

peroxide,  50 

sulphide,  106 
Hydrophobia,  449 
Hydroxides,  192 
Hygiene,  426 
Hypocotyl,  285 

Ice,  83,  84 

box,  64 

Igneous  rocks,  262,  263 
Illuminating  gas,  116,  225 
Image,  151,  157,  415 
Incandescent  mantles,  225 
Inch,  7 

Incidence,  angle  of,  156 
Inclined  plane,  174,  180 
Induction,  127,  132 
Inertia,  26 
Infection,  429 
Ink  stains,  204 
Inoculation,  445 
Insects,  322 
Inspiration,  381 
Insulation,  228 
Insulators,  131 
Intestines,  357 
Iris,  417 
Iron,  50,  265 

in  soil,  275 

rust,  204 

salts,  tests  for,  195 
Irrigation,  43,  273 
Isobars,  251 
Isotherm,  255 

Joints,  341 

Keramics,  260 
Kerosene,  115 

lamps,  224 

stoves,  213 
Kidneys,  366,  379 
Kilowatt,  229 
Kindling,  a  fire,  210 

temperature,  68 
Kite,  184 

Lachrymal  glands,  417 
Lacteal  glands,  358 


Lactic  acid,  116,  189 
Lampblack,  112 
Lamps,  kerosene,  224 
Land  plaster,  278 
Larynx,  383,  384 
Laundry,  197 
Lavoisier,  46 
Lava,  261 
Law  of  winds,  245 
Lead,  190,  209 
Leaves,  285,  286,  288 

work  of,  287 
Legumen,  348 
Lens,  159,  416 
Lever,  174,  176,  177,  345 
Levulose,  349 
Leyden  jar,  133 
Lichens,  304 
Liebig's  condenser,  80 
Ligaments,  341,  345,  418 
Light,  141,  151,  159,429,453 

in  the  house,  221 

intensity  of,  153 

waves,  9 
Lighting,  acetylene  for,  227 

artificial,  223 

electric,  228 

gas  for,  224 
Lightning,  134 
Light-year,  10 
Lime,  in  soil,  279 

kiln,  123 

slaked,  192 
Limewater,  51,  118 
Limestone,  121,  259,  261,  340 

in  soil,  279 
Linen,  201,  307 
Linseed  oil,  203 
Liquefying  of  gases,  68 
Liquid  air,  56 
Liquids,  66 
Liquid,  surface  of,  29 

ammonia,  84 
Liter,  9 
Litmus,  190 
Liver,  357,  358 
Lizard,  329 
Loam,  269 
Lobster,  321 


INDEX 


479 


Lodestones,  125 

Luminous  bodies,  150 

Lungs,  52,  376,  379,  380,  381 

Lye,  192,  200 

Lymph,  350,  366,  373,  378,  379 


Machines,  174 
Magnesium  in  soil,  275 
Magnetic,  field,  127 

poles,  128 
Magnets,  17,  125 
Magnifying  lens,  165 
Malic  acid,  189 
Maltose,  349,  361,  362 
Mammals,  331,  338 
Man,  334,  338 
Manganese  dioxide,  50 
Manometer,  226 
Mantle,  incandescent,  225 

rock,  256,  258 
Maple,  294 
Marble,  122,  191,  262 
Marsh  gas,  114 
Mass,  18,  20,  32 

center  of,  34 
Match,  6,  69 
Matches,  friction,  210 

parlor,  210 

safety,  211 
Matter,  4 
Measles,  448 
Medulla  oblongata,  398 
Memory,  405 
Mercuric  iodide,  454 
Meniscus,  30 
Mercuric  oxide,  46,  49, 
Mercury,  29,  40,  46,  56 

chloride,  453 

fulminate,  22 
Metacarpals,  344 
Metals,  98 

corrosion,  190 

oxides,  190 

Metamorphic  rocks,  262,  263 
Metamorphosis,  322 
Metatarsals,  344 
Meteorology,  249 
Meter,  7,  8 


Meter,  electric,  228 

gas,  226 

water,  209 

Metric  system,  7,  9,  12,  13 
Method,  scientific,  2,  3 
Mica,  221,  259 
Microbes,  303 
Microscope,  165 
Midbrain,  399 
Mildew,  304 
Milk,  88,  432 
Mind,  399,  410 
Minerals,  98,  347 
Mirrors,  156 
Mixtures,  97 

Modern  conveniences,  207 
Modified  leaves,  288 
Moisture  of  air,  235 
Moisture  in  air,  need  of,  220 
Molecules,  60 
Mollusks,  319 
Monsoons,  246 
Moonlight,  150,  158 
Mordants,  203 
Morse,  S.  F.  B.,  140 
Mortar,  123 

Mosquito,  323,  426,  429 
Mosses,  301,  304 
Moths,  323 
Motors,  electric,  145 
Mould,  304 
Mouth,  351 
Mucus,  350 
Muriatic  acid,  105 
Muscle,  340,  344 
Mushrooms,  304 
Mussel,  319 
Myosin,  348 

Nails,  389 
Natural  gas,  114 
Nature,  1 
Nerve  cells,  396 

tissue,  340,  396 
Nervous  system,  395,  402 
Neuron,  396,  404 
Neutralization;  Salts,  193 
Newton,  Sir  Isaac,  17,  161 
Niagara,  261 


480 


INDEX 


Nitrates,  tests  for,  195 
Nitric  acid,  189,  190 
Nitrogen,  47,  53 

in  fertilizers,  279 

in  soil,  275,  277,  279 
Nitroglycerine,  54 
Nodes,  289 
Noise  and  tone,  170 
Nose,  383 
Nucleus,  303,  313 
Number  of  elements,  107 

Obsidian,  288 
Oils,  198,  349 
Oleic  acid,  361 
Opaque  bodies,  150 
Opium,  367 
Ores,  112 
Organs,  3 
Ounce,  12 
Ovary,  298 
Ovule,  298 
Oxidation,  48,  52 
Oxides,  48 

of  metals,  190 
Oxygen,  46,  49,  50,  95,  96,  164 

in  soil,  275 
Oyster,  319 

Paint,  112,  203 
Palate,  354,  384 
Pancreas,  357,  359 
Paper,  116 
PapiUae,  389 
Paraffin,  115,  204 
Paramecium,  314 
Parasite,  303 
Patella,  344 
Patent  medicines,  367 
Pearls,  320 
Pelvis,  343 
Penumbra,  153 
Pepsin,  356,  359,  361 
Peptones,  359,  362 
Percussion,  22 
Pericardium,  373 
Periosteum,  340 
Perspiration,  71,  389,  391 
Petiole,  285 


Petroleum,  114 
Phalanges,  344 
Pharynx,  353,  383 
Phenomena,  2 
Phosphates,  278,  340 

tests  for,  195 
Phosphoric  acid,  189 
Phosphorus,  53,  210 

in  soil,  275,  277 

oxide,  53 

sulphide,  211 
Photography,  195 
Photometer,  154 
Physical  changes,  94,  265 
Physical  states  of  matter,  65 
Physiology,  338 
Pisa,  Leaning  Tower  of,  19,  20 
Pistil,  298 
Piston,  23,  42 
Pitch,  170,  386 
Pith,  291 
Planets,  27 

Plants,  57,  266,  282,  283,  301,  307 
Plasma,  377 
Plaster,  123 
Platinum,  96 
Plexus,  401 
Plowing,  271 
Plumbing,  209 
Plumbline,  20 
Plumule,  285 
Pneumatic  hammer,  44 
Pneumonia,  448 
Polaris,  10 
Poles  of  battery,  96 
Pollen,  297,  298 
Polyps,  315 
Pons,  399 
Porcelain,  260 
Potash,  191 
Potassium,  carbonate,  191,  194 

chlorate,  49 

chloride,  191 

hydroxide,  192,  194 

in  fertilizers,  278 

in  soil,  275,  277 

permanganate,  50 

salts,  tests  for,  196 
Pound,  12 


INDEX 


481 


Power,  25 
Preservation,  435 
Pressure,  atmospheric,  39 

of  air,  233,  248 

reduced,  87 

standard,  40 
Priestley,  46 
Printer's  ink,  112 
Prism,  160 
Properties,  5,  6 
Proteids,  55,  347,  356,  362 
Proteoses,  356,  362 
Protoplasm,  286,  302,  377 
Prussic  acid,  116 
Ptomaines,  428 
Ptyalin,  352,  359,  361 
Pulley,  174,  178 
Pulmonary  circulation,  373 
Pulse,  375 
Pumice,  261,  263 
Pumps,  39,  41,  42,  43 
Pupa,  323 
Pylorus,  355 
Pyrometer,  14 
Pyrogallic  acid,  166 

Quarantine,  450 
Quarter  sawing,  293 
Quartz,  259,  261 
Quicklime,  94,  192 

Rabies,  449 
Radial  sawing,  292 
Radiation,  63 
Radius,  344 
Rain,  57,  240 
Rainbow,  161 
Rainfall,  241,  250 
Rain  gauge,  241 
Reaction,  alkaline,  192 
Receptacle  of  flower,  297 
Reduced  pressure,  87 
Reflected  light,  155,  156 
Reflection,  angle  of,  156 
Reflex  action,  404 
Refraction,  of  light,  158 

of  sound,  159 

Relative  humidity,  236,  237 
Rennin,  356,  359 


Reptiles,  328 

Reservoirs,  274 

Residual  mantle  rock,  266 

Residual  soil,  270 

Resistance,  141,  142 

Respiration,  39,  51,  52,  376,  379 

Retina,  415,  417 

Retort,  47 

Ribs,  343 

Rocks,  258,  259,  260 

Rock  salt,  102 

Roots,  295 

Rootstock,  291 

Rotation  of  crops,  277 

Rusting,  39,  48,  50 

Safety  lamp,  miner's,  114 

Sailboat,  182 

Sal  ammoniac,  105 

Sal  ammoniac  cell,  138 

Saliva,  351 

Salt,  87,  89,  90,  91,  102,  349 

Salts,  193,  194 

tests  for,  194,  195,  196 
Sand  blast,  43 
Sand  dune,  265 
Sandstone,  259 
Sap,  294 
Saprophyte,  303 
Saturation,  235 
Scapulas,  343 
Scarlet-fever,  447 
Science,  1,  3 

general,  3 

Scientific  method,  2,  3 
Screw,  174,  181 
Secretion,  351,  366,  377,  379 
Sedentary  soil,  270 
Sedimentary  rocks,  261 
Seeds,  297,  298,  299,  301 
Sense  organs,  399 
Senses,  special,  409 
Sepals,  297 
Separator,  dairy,  27 
Serum,  444 
Shadows,  152 
Shale,  259 
Sight,  409,  415 
Silicon  in  soil,  275 


482 


INDEX 


Silk,  204 

Silver  chloride,  166,  195 

Silver-plating,  143 

Skeleton,  342 

Skin,  388,  391,  410 

Skull,  342 

Sky  colors,  162 

Slaked  lime,  118 

Slate,  262 

Slugs,  320 

Smallpox,  444 

Smell,  409,  412 

Smoke,  213 

Snakes,  328 

Snow,  91,  240 

Soap,  79,  197,  198,  200 

Soda,  caustic,  103 

washing,  191 

baking,  191 

water,  118 
Sodium,  103 

carbonate,  198 

chloride ;  salt,  191,  194 

hydroxide,  103,  192 

in  soil,  275 

nitrite,  54 

salts,  tests  for,  195 
Soil,  258,  267,  269,  270 
Solar  plexus,  401 
Solids,  65 
Solubility,  89 
Solute,  87 
Solutions,  87,  88 
Solvent,  87 
Soot,  112 
Sound,  167,  168 

reflection  of,  156 

refraction  of,  159 

velocity  of,  151 
Sources  of  heat,  72 
Space,  4,  5,  6 
Specific  heat,  70 
Specific  gravity,  31,  32 
Spectrum,  solar,  161 
Speech,  386 
Spinal  cord,  399 
Sponges,  315 
Spore,  302 
Sprain,  346 


Stains,  removal  of,  204 
Stalactites,  122 
Stalagmites,  122 
Stamens,  298 
Starch,  116,  287,349 
Starfishes,  316 

Stars,  apparent  position,  158 
Steam,  85 

engine,  23 

heating,  214,  215 
Steapsin,  360,  361 
Stearic  acid,  361 
Stems,  289,  290 
Sternum,  343 
Stigma,  298 
Stipules,  285 
Stomach,  355 
Stomata,  286 
Stoneware,  260 
Stoves,  210 

electric,  214 

gas,  213 

gasoline  and  kerosene,  213 
Stratified  rocks,  261,  262 
Stratum,  261 
Style,  298 
Submarine  boat,  44 
Subsoil,  269 
Substances,  5 
Sugar  refining,  87 
Sugars,  116,  349 
Sulphates,  194,  195 
Sulphur,  5,  51,  106,  210 

dioxide,  51,  106,  454 
Sulphuric  acid,  95,  189 
Sulphur  in  soil,  275 
Sun,  72 

distance  of,  9 
Sunlight,  57 

Suspended  substances,  81 
Switch,  electric,  228 
Sympathetic  (nervous)  system,  395, 
400 

Talus,  264 
Tap  root,  295 
Tarsals,  344 
Tartaric  acid,  189 
Taste,  409,  411 


INDEX 


483 


Teeth,  352,  427 
Telegraph,  139 
Telephone,  170 
Temperature,  62 
Tendons,  345 
Testa,  284 
Tests  for  salts,  194 
Tetanus,  449 
Thermometer,  14,  60,  61 
Thermos  bottles,  56 
Thermostat,  215 
Thirst,  410 
Thorax,  338,  373 
Thunder,  134 
Thunderstorms,  247 
Tibia,  344 
Tincture,  87 
Tinder,  210 
Tissue,  339,  396 
Tobacco,  387,  406 
Tonsils,  384 
Tornadoes,  247,  248 
Torricelli,  39 
Touch,  409,  410 
Toxins,  278,  428 
Trachea,  354,  383,  384 
Trade  winds,  246 
Translucent  bodies,  151 
Transparent  bodies,  150 
Traps  and  Hydrants,  209 
Trichinae,  364 
Trolley  cars,  145 
Trypsin,  360,  361 
Tubercles,  55 
Tuberculosis,  347,  440 

treatment  of,  217 
Turbines,  146 
Turpentine,  203 
Turtle,  328 
Tympanum,  413 
Typhoid,  437,  447 
Typhoons,  249 


Ulna,  344 
Umbra,  153 
Units  of  length,  7,  9 
Univalves,  320 
Uric  acid,  366 


Vaccination,  445 

Vacuum,  6,  20,  40,  67 

Vaporizer,  214 

Vaseline,  115 

Velocity,  22 

Vein,  372,  374 

Veins,  of  leaves,  285 

Ventilation,  217,  218,  219,  220 

Ventricle,  373 

Vertebrates,  325 

VilU,  357 

Vinegar,  188 

Vitreous  humor,  417 

Voice,  385 

Volcanic  conditions,  263 

Volta,  136 

Voltaic  cell,  136 

Volume,  6,  7 

Voluntary  action,  404 

Vorticella,  314 

Washing,  of  clothing,  197 

powders,  201 

soda,  191 
Water,  28,  232,  347 

hardness  of,  79,  121 

composition  of,  95 

electrolysis  of,  95 

expansion,  266 

gas,  225 

hard,  200 

in  house  and  town,  207 

in  soil,  270 

occurrence  of,  76 

purity  of,  77 

Waters,  natural,  composition  of,  77 
Waterspouts,  248 
Watt,  James,  25,  228 
Waves,  163 
Waxes,  223 
Weather,  232 

Bureau,  249 

forecast,  251 

Weathering  of  rocks,  264,  265 
Weather  maps,  251 
Weather  service  in  U.  S.,  249 
Wedge,  174,  180 
Weight,  4,  5,  10,  18 
Weight,  units  of,  11,  12 


484 


INDEX 


Wells,  pollution  of,  78 

Wheat,  271 

Wheel  and  axle,  174,  179 

Whirlwind,  246,  248 

White  lead,  203 

Wind,  22,  57,  233,  245,  246 

Windmill,  185 

Wind,  use  of,  183,  184,  185 

Wood,  116,291,294 

Wood  alcohol,  116,  117 


Work,  24,  25 

chemical,  164 
Worms,  317 

Yard,  7 

Yellow  fever,  449 
Yeast,  119,  188 
Yeast  plant,  303 

Zenith,  159 


14  DAY  USE 

TJRN  TO  DESK  FROM  WHICH  BORROWED 

LOAN  DEPT. 

RENEWALS  ONLY— TEL.  NO.  642-3405 

This  book  is  due  on  the  last  date  stamped  below  or 

on  the  date  to  which  renewed. 
Kenewed  books  are  subject  to  immediate  recall. 

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